qemu-log: default to stderr for logging output

Switch the default for qemu_log logging output from "/tmp/qemu.log"
to stderr. This is an incompatible change in some sense, but logging
is mostly used for debugging purposes so it shouldn't affect production
use. The previous behaviour can be obtained by adding "-D /tmp/qemu.log"
to the command line.

This change requires us to:
 * update all the documentation/help text (we take the opportunity
   to smooth out minor inconsistencies between the phrasing in
   linux-user/bsd-user/system help messages)
 * make linux-user and bsd-user defer to qemu-log for the default
   logging destination rather than overriding it themselves
 * ensure that all logfile closing is done via qemu_log_close()
   and that that function doesn't close stderr
as well as the obvious change to the behaviour of do_qemu_set_log()
when no logfile name has been specified.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-id: 1361901160-28729-1-git-send-email-peter.maydell@linaro.org
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/qemu-doc.texi b/qemu-doc.texi
index 6d7f50d..747e052 100644
--- a/qemu-doc.texi
+++ b/qemu-doc.texi
@@ -2642,8 +2642,8 @@
 Debug options:
 
 @table @option
-@item -d
-Activate log (logfile=/tmp/qemu.log)
+@item -d item1,...
+Activate logging of the specified items (use '-d help' for a list of log items)
 @item -p pagesize
 Act as if the host page size was 'pagesize' bytes
 @item -g port
@@ -2781,8 +2781,8 @@
 Debug options:
 
 @table @option
-@item -d
-Activate log (logfile=/tmp/qemu.log)
+@item -d item1,...
+Activate logging of the specified items (use '-d help' for a list of log items)
 @item -p pagesize
 Act as if the host page size was 'pagesize' bytes
 @item -singlestep