docs: update MESA_DEBUG envvar documentation.

silent, flush, incomplete_tex and incomplete_fbo flags were not
documented (see src/mesa/main.debug.c for more info).

FP is not checked anymore.

v2 (Brian Paul):
 * MESA_DEBUG accepts a comma-separated list of parameters.
 * Clarify how MESA_DEBUG behaves with mesa debug and release builds.
 * Updated wording.

v3: Better wording for one paragraph (Brian Paul)

Reviewed-by: Brian Paul <brianp@vmware.com>
1 file changed