Better error handling for font config reading

The code is still quite experimental and sometimes generate errors while it could still continue.
Warning if a file cannot be read in font conf
Adding semibold as a synonym for bold, not sure it's useful...
Updating NEWS file
Adapting math test for LuaTeX > 0.74
Make \font\foo=file:xxx more reliable

We use the same function (fonts.names.resolve) for both name and
file specification, as the database search is much better than a simple
filename resolving (it might contain more entries), it's also
easier to spot a problem.
Preventing loop-references in fontconfig files

I just had this case on a recent Ubuntu...
Removing the todo of previous commit
Making tests useable by non-ConTeXt users
More tests availability
I had forgotten this check for reference-looping
Updating NEWS
Merge pull request #2 from eroux/texlive2011

Texlive2011
remove unnecessary table indexing