Merge branch 'ml/cygwin-updates'

The tip one does _not_ revert c869753e (Force core.filemode to
false on Cygwin., 2006-12-30) on purpose, so that people can
still retain the old behaviour if they wanted to.

* ml/cygwin-updates:
cygwin: stop forcing core.filemode=false
Cygwin 1.7 supports mmap
Cygwin 1.7 has thread-safe pread
Cygwin 1.7 needs compat/regex