Merge changes I7352dc43,Icc1c3225,Idd0e4950,I5b709c56,Ia12bbb4d, ...

* changes:
  vl-android.c: Support EXT4 cache partitions.
  android/filesystems/partition_types.h: new header
  Support EXT4 cache partition images.
  Add android_createEmptyExt4Image()
  distrib/ext4_utils: new third-party library sources.
  distrib/libselinux: Add new third-party library sources.
  distrib/libsparse: Add new third-party library sources.
  distrib/zlib-1.2.8: Build as static libraries.