Fixes glVertexAttribIPointer on GLES.

We need to pull in function pointers for OpenGL 3.0 in order to use glAttribIPointer.
This isn't too big of an issue, and this code will be gone in the future when we change over to libepoxy.
Just need to push code upstream to libepoxy to support Android with GLES and GL first.
Changes posmtx vertex attribute to integer.

This makes it so we don't need to do some dumb casting from float to integer in our shaders.
Only tested in OpenGL, needs to be tested in D3D.
Merge pull request #310 from Sonicadvance1/Integer-posmtx

Change over to use integer posmtx in our vertex shaders