Revert "5097 - Menu corrupted on start (on IRIX)"

Calling glClear( any bits ) in GL_SetDefaultState makes connect screen black using the proprietary NVidia driver on Windows and GNU/Linux.

This reverts commit 92573270de98a20cd78842bd2043cfe07bc5b2e1.
Drop sounds starting with * before allocating sfx slot

Causes handle 0 to be returned by S_RegisterSound.
OpenGL2: Fix TCGEN_ENVIRONMENT stages not rendering correctly.
OpenGL2: Clean up texmod calculations, and improve vertex animation handling.
OpenGL2: Use an idea from ETXreal and separate world VBO into separate VBOs by shader.
OpenGL2: Merge bsp surface structs into a single struct, and more cleanup.