ogl: Refactor GLES bitmap locking code like the desktop version.
ogl: Remove POT hack when unlocking non-backbuffer bitmap region on Android.

This fixes the non-backbuffer READWRITE test in ex_lockbitmap on a Nexus 7,
otherwise it writes back too much to the target bitmap.
The Nexus 7 doesn't require the corresponding POT roundup at lock time
either, but I left that in for now.
ogl: Use alternative path for unlocking a backbuffer region on Android.

The existing code path for updating a region of the backbuffer on
Android was using glDrawTex.  However, on a Nexus 7 device, all I could
see what that it drew a solid rectangle at the specific position and
dimensions.

There already exists an alternative path that Trent had written for the
Raspberry Pi.  I find that code quite ugly, but at least it makes
some examples like ex_lockbitmap work better on the Nexus 7,
so I'm enabling it for Android.
ogl: Use inverted y parameter in call to glDrawTex.

This fixes the positioning of the solid rectangle drawn by glDrawTex,
even if I couldn't manage to get it to draw the pixel data.
ogl: Clean up FBO creation during bitmap locking.

This was previously done by calling al_set_target_bitmap() for its
side-effect, yuck.
ogl: Propagate errors up lock bitmap implementations.
All but remove ALLEGRO_FORCE_LOCKING flag.

There doesn't seem to be a reason for it and there was no objection so
just ignore it and deprecate it.  An earlier change to the GLES bitmap
locking implementation already used an FBO on some path in spite of the
flag.
ex_bitmap_target: Delete.

It was only to test ALLEGRO_FORCE_LOCKING (or vice versa?) which has
just been neutered.
ex_lockbitmap: Refactor.
ex_lockbitmap: Support touch input.
ex_lockbitmap: Test READWRITE mode by leaving some pixels untouched.
ex_blend: Support touch input.
ex_nodisplay: Clear memory bitmap.
ex_loading_thread: Add missing synchronisation between threads.
ex_physfs: Work on Android by reading from APK directly.
cmake: Let clang use same options as gcc in build system.
x11: Fix clang warning.
acodec: Seeking in wavs would always have returned success.
ex_synth: Delete unused private field.
cosmic_protector: Delete unused private field.