Let users select their pythons

Add configure check for python, exit if not found. Add switches
for specifying the path to python, use the path in Makefile.

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

Makefile

diff --git a/Makefile b/Makefile
index f3a03ad..daa3aa0 100644
--- a/Makefile
+++ b/Makefile
@@ -168,22 +168,22 @@
 
 $(qapi-dir)/test-qapi-types.c: $(qapi-dir)/test-qapi-types.h
 $(qapi-dir)/test-qapi-types.h: $(SRC_PATH)/qapi-schema-test.json $(SRC_PATH)/scripts/qapi-types.py
-	$(call quiet-command,python $(SRC_PATH)/scripts/qapi-types.py -o "$(qapi-dir)" -p "test-" < $<, "  GEN   $@")
+	$(call quiet-command,$(PYTHON) $(SRC_PATH)/scripts/qapi-types.py -o "$(qapi-dir)" -p "test-" < $<, "  GEN   $@")
 $(qapi-dir)/test-qapi-visit.c: $(qapi-dir)/test-qapi-visit.h
 $(qapi-dir)/test-qapi-visit.h: $(SRC_PATH)/qapi-schema-test.json $(SRC_PATH)/scripts/qapi-visit.py
-	$(call quiet-command,python $(SRC_PATH)/scripts/qapi-visit.py -o "$(qapi-dir)" -p "test-" < $<, "  GEN   $@")
+	$(call quiet-command,$(PYTHON) $(SRC_PATH)/scripts/qapi-visit.py -o "$(qapi-dir)" -p "test-" < $<, "  GEN   $@")
 $(qapi-dir)/test-qmp-commands.h: $(qapi-dir)/test-qmp-marshal.c
 $(qapi-dir)/test-qmp-marshal.c: $(SRC_PATH)/qapi-schema-test.json $(SRC_PATH)/scripts/qapi-commands.py
-	    $(call quiet-command,python $(SRC_PATH)/scripts/qapi-commands.py -o "$(qapi-dir)" -p "test-" < $<, "  GEN   $@")
+	    $(call quiet-command,$(PYTHON) $(SRC_PATH)/scripts/qapi-commands.py -o "$(qapi-dir)" -p "test-" < $<, "  GEN   $@")
 
 $(qapi-dir)/qga-qapi-types.c: $(qapi-dir)/qga-qapi-types.h
 $(qapi-dir)/qga-qapi-types.h: $(SRC_PATH)/qapi-schema-guest.json $(SRC_PATH)/scripts/qapi-types.py
-	$(call quiet-command,python $(SRC_PATH)/scripts/qapi-types.py -o "$(qapi-dir)" -p "qga-" < $<, "  GEN   $@")
+	$(call quiet-command,$(PYTHON) $(SRC_PATH)/scripts/qapi-types.py -o "$(qapi-dir)" -p "qga-" < $<, "  GEN   $@")
 $(qapi-dir)/qga-qapi-visit.c: $(qapi-dir)/qga-qapi-visit.h
 $(qapi-dir)/qga-qapi-visit.h: $(SRC_PATH)/qapi-schema-guest.json $(SRC_PATH)/scripts/qapi-visit.py
-	$(call quiet-command,python $(SRC_PATH)/scripts/qapi-visit.py -o "$(qapi-dir)" -p "qga-" < $<, "  GEN   $@")
+	$(call quiet-command,$(PYTHON) $(SRC_PATH)/scripts/qapi-visit.py -o "$(qapi-dir)" -p "qga-" < $<, "  GEN   $@")
 $(qapi-dir)/qga-qmp-marshal.c: $(SRC_PATH)/qapi-schema-guest.json $(SRC_PATH)/scripts/qapi-commands.py
-	$(call quiet-command,python $(SRC_PATH)/scripts/qapi-commands.py -o "$(qapi-dir)" -p "qga-" < $<, "  GEN   $@")
+	$(call quiet-command,$(PYTHON) $(SRC_PATH)/scripts/qapi-commands.py -o "$(qapi-dir)" -p "qga-" < $<, "  GEN   $@")
 
 test-visitor.o: $(addprefix $(qapi-dir)/, test-qapi-types.c test-qapi-types.h test-qapi-visit.c test-qapi-visit.h) $(qapi-obj-y)
 test-visitor: test-visitor.o qfloat.o qint.o qdict.o qstring.o qlist.o qbool.o $(qapi-obj-y) error.o osdep.o qemu-malloc.o $(oslib-obj-y) qjson.o json-streamer.o json-lexer.o json-parser.o qerror.o qemu-error.o qemu-tool.o $(qapi-dir)/test-qapi-visit.o $(qapi-dir)/test-qapi-types.o

configure

diff --git a/configure b/configure
index 600da9b..38e3724 100755
--- a/configure
+++ b/configure
@@ -475,6 +475,7 @@
 
 : ${make=${MAKE-make}}
 : ${install=${INSTALL-install}}
+: ${python=${PYTHON-python}}
 
 if test "$mingw32" = "yes" ; then
   EXESUF=".exe"
@@ -516,6 +517,8 @@
   ;;
   --install=*) install="$optarg"
   ;;
+  --python=*) python="$optarg"
+  ;;
   --extra-cflags=*)
   ;;
   --extra-ldflags=*)
@@ -924,6 +927,7 @@
 echo "  --extra-ldflags=LDFLAGS  append extra linker flags LDFLAGS"
 echo "  --make=MAKE              use specified make [$make]"
 echo "  --install=INSTALL        use specified install [$install]"
+echo "  --python=PYTHON          use specified python [$python]"
 echo "  --static                 enable static build [$static]"
 echo "  --mandir=PATH            install man pages in PATH"
 echo "  --datadir=PATH           install firmware in PATH"
@@ -1084,6 +1088,13 @@
   fi
 fi
 
+if has $python; then
+  :
+else
+  echo "Python not found. Use --python=/path/to/python"
+  exit 1
+fi
+
 if test -z "$target_list" ; then
     target_list="$default_target_list"
 else
@@ -2591,6 +2602,7 @@
 echo "LDFLAGS           $LDFLAGS"
 echo "make              $make"
 echo "install           $install"
+echo "python            $python"
 echo "host CPU          $cpu"
 echo "host big endian   $bigendian"
 echo "target list       $target_list"
@@ -3003,6 +3015,7 @@
 echo "INSTALL_DIR=$install -d -m0755 -p" >> $config_host_mak
 echo "INSTALL_DATA=$install -m0644 -p" >> $config_host_mak
 echo "INSTALL_PROG=$install -m0755 -p" >> $config_host_mak
+echo "PYTHON=$python" >> $config_host_mak
 echo "CC=$cc" >> $config_host_mak
 echo "CC_I386=$cc_i386" >> $config_host_mak
 echo "HOST_CC=$host_cc" >> $config_host_mak