fixes #169 - allow a negative step in xrange
Documentation updates
Build process update: make clang link against our new libstdc++

Previously it would always link against the system libstdc++; not sure how
that was working.

Also, put that in its own included makefile so that we can track the dependence
on the configuration parameters (otherwise you would have to run a configuration
manually to get this change).
Rebase LLVM rev
Merge remote-tracking branch 'upstream/master'
adds test cases for xrange with a negative step and xrange(0)
Merge pull request #176 from dagar/master

fixes #169 - allow a negative step in xrange
Stopgap for rewrite-being-too-large

Just let the rewrite continue but stop emitting any assembly,
and then at the end abort the rewrite.
add cmake generated files to .gitignore
initial CMakeLists.txt to build pyston
cmake link curses and lzma directly (don't try to find_package())