Added android/config.h which will be used to configure
android builds of libraries. Currently I've undef HAVE_HASH_MAP
and HAVE_HASH_SET as the versions in stlport generated compile
errors.

Updated .gitignore to be more selective on what it ignores so
android/config.h wouldn't be ignored.

Change-Id: I53f3636121db2c6017491a37998b816aaf0cab5d