Fix two constants in GLSL shaders. Remove f suffix from float and fix
int to float assignment. They were causing shader compile errors in
OpenGL ES 2 context.
Remove disabling clip plane. Clip plane is unused and never enabled in
the opengl2 renderer. Remove disabling it to avoid causing a GL error
when using OpenGL 3.2 core profile or OpenGL ES.
Make VAO cache vertex stride be size of srfVert_t since that is what
is uploaded to the GPU. No behavior change. There is a disabled debug
id in srfVert_t though which if enabled changes srfVert_t size.
OpenGL ES is only required to support unsigned short for element buffer
values.
R_DrawElements() firstIndex argument was glIndex_t which caused element
indexes to wrap around to 0 when glIndex_t is an unsigned short.
(glIndex_t is an index into the vertexes buffer, not element buffer.)
Change it to 'int' like tess.firstIndex which is passed to
R_DrawElements().
World VAO cache buffer size allowed storing more vertexes than unsigned
short glIndex_t could reference. This resulted in the vertex indexes in
the element buffer wrapping around to 0.
