Revert the TeX-XeT changes

Was too invasive and too experimental to use by default, so revert back
to the original code for now.
Revert "Disable synctex for now"

This reverts commit 0fc086de1aaaab45af2d14945b7b48c770696a9c.
Make SyncTeX build and remove files we don’t use
Don’t accept Graphite features without a setting

Now that I understand Graphite a bit better, I can see why the original
code ignored features like:

  \font\krishnaalt="Krishna Tamil/GR:Classical Orthography"

where it should be specified as:

  \font\krishnaalt="Krishna Tamil/GR:Classical Orthography=True"

I thought i’d accept the first form to mean an OpenType-like feature
activation, but this makes no sense in Graphite, quoting Matrin on the
mailing list:

 “There is no OpenType concept of activation or not of a feature. Think
  more along the lines of AAT or user features. A feature is just a
  value setting within the font that the graphite code can query to
  change how it behaves. Thus all features are activated, it's just what
  their value is.”

So the user really has to provide a feature setting (value) to alter the
existing one.
Fix \XeTeXisdefaultselector with Graphite fonts
Don’t try to get glyph names from ‘post’ table

We already have code to get the glyph names from FreeType/Core Text and
they do better job than us (e.g. read names from CFF table), and I doubt
the default implementation is ever executed, so lets just drop it.
XeTeX: extract etex_version.h from xetex.web

git-svn-id: svn://tug.org/texlive/trunk/Build/source@29225 c570f23f-e606-0410-a88d-b1316a301751
Inherit XeTeXFontInst_Mac from XeTeXFontInst_FT2

So that we can share the FreeType code especially for HarfBuzz, right
now on Mac HarfBuzz uses FreeType when fonts are loaded by file name and
our Core Text-based font functions when fonts are loaded by font name,
which is not good.
Remove now unused HarfBuzz font functions
Use XeTeXFontInst_FT2 for those
Revert "Implement variation selectors support"

This reverts commit 835fce61e79983a314e0866c01fb6ad502c54ff2
Make few functions static
Merge XeTeXFontInst_FT2.cpp into XeTeXFontInst.cpp
Get ‘post’ table from FreeType
Unused typedef's
Drop font table caching

There is no much point in it now.
Get more tables from FreeType
Drop no longer used header
Unused #includes
Minor