Fix bug where files containing Windows line endings were not handled
correctly. This also removes '\n' from the end of the lines when
doing comparisions.
Added --param=python_exec=<path to python> option to lit tests so
we can easily change python interpreter
Fix bug for python2 when parsing the CHECK directives in a file with
dos line endings. The extra line ending character would become
part of the regex pattern which would mean it wouldn't match
anything!