Add the interface for safe GL context wrapping and implement on Mac.

Linux implementation will come next.
Merge pull request #6 from pcwalton/gl-context

Add the interface for safe GL context wrapping and implement on Mac.
Add Linux offscreen GL context support, untested
Update the Linux functionality to use ARCs and make the Mac match.

GLX contexts are not reference counted, so we must do the reference
counting ourselves, in Rust.
Merge pull request #7 from pcwalton/linux-arc

Update the Linux functionality to use ARCs and make the Mac match.
Merge remote branch 'origin/master-upgrade' into HEAD

Conflicts:
	platform/macos.rs
Add extern mod extra;
support android build
Merge pull request #9 from webconvforge/PRbase

support android build
Update to latest Rust
Merge pull request #10 from kmcallister/rust-upgrade

Update to latest Rust
More Rust version updates

macos.rs changes are untested.
Merge pull request #11 from kmcallister/rust-upgrade

More Rust version updates
Link libGL on Linux

Needed to run tests.
Merge pull request #12 from kmcallister/rust-upgrade

Link libGL on Linux
Warning police.
Merge branch 'master-upgrade'.

We were missing one android related commit on master.

Conflicts:
	sharegl.rc
Update for language changes