This patch adjusts the aliasing pattern in the GL API description XML,
and the functions that implement the GL API within Mesa, to
consistently follow these naming conventions:

- When several function names are aliases of each other, the primary
  name is the one with no extension suffix (or the name with the
  suffix "ARB", if no unsuffixed name is available).  (By "primary
  name", I mean the name that all the other functions point to using
  the XML "alias" attribute).

- The name of the mesa implementation of each function is the same as
  the primary name, with the prefix "_mesa_".

This patch renames the following mesa functions:
  _check_GetTexGenxvOES => _mesa_GetTexGenxvOES
  _check_TexGenxOES => _mesa_TexGenxOES
  _check_TexGenxvOES => _mesa_TexGenxvOES
  _es_AlphaFuncx => _mesa_AlphaFuncx
  _es_ClearColorx => _mesa_ClearColorx
  _es_ClearDepthx => _mesa_ClearDepthx
  _es_ClipPlanef => _mesa_ClipPlanef
  _es_ClipPlanex => _mesa_ClipPlanex
  _es_Color...