Fix error checking bugs in load_shader.

This code was failing on Android because of an error flag set during an
earlier operation (`enable(TEXTURE_2D)`).  The logging was also broken because
get_error was called twice.
Fix compiler warnings on Android
Merge pull request #92 from mbrubeck/android-err

Android build and crash fixes
Fix use-after-free on Android.

Fixes servo/servo#2916 (broken rendering on Android), which happened because
the `bitmap` pointer outlived the Vec<u8> that it pointed to.
Make NativeSurface::upload a mut method
Replace transmute with as and as_mut_slice
Merge pull request #95 from mbrubeck/android-bitmap

Fix use-after-free on Android.
Upgrade Rust.
Merge pull request #94 from mrobinson/more-cleanup

Move get_buffer_requests into rust-layers from Servo
Merge pull request #96 from servo/rustup-20140716

Upgrade Rust.
Generate documentation with rustdoc
Upgrade Rust.
Merge pull request #99 from servo/rustup-20140804

Upgrade Rust.
Merge pull request #98 from servo/rustdoc

Generate documentation with rustdoc
Add GLSL precision specifier for android.
Merge pull request #100 from glennw/android-fix

Add GLSL precision specifier for android.
Track content_age of LayerBuffer in the struct itself

Instead of relying on the TileGrid to track content age, just store the
information in the LayerBuffer itself. This means that we must pass it
with BufferRequests as well, so that the renderer can populate th
LayerBuffer properly.
Add a method marking all tiles as having changed contents