Rename the settings that control them to be more descriptive
Remove the separate boolean setting (RenderUseImpostors) that governed both
Establish default values based on gpu class for impostors and visual muting
* Modified mac feature table to bring it up to date with latest renderer features including deferred rendering
* Changed mac AGL pixel format to no longer allow it to revert to software rendering when shader compilation errors occur.
* Fixed up various GLSL shader compilation warnings and errors that came up as a result of the above changes.
* Changed initial conditions for the "hardware skinning" checkbox on the preferences floater so it can be modified before login on machines that support avatar vertex programs.
* Removed unused avatarAlphaF.glsl files
Reviewed by davep
windlight14 which have passed QA (up through r79932).
svn merge -r 80831:80833 svn+ssh://svn.lindenlab.com/svn/linden/branches/merge_windlight14_r80620
Oz Linden