fix issue 1763: strip chars from end of line when parsing gitpatch lines

issue1251: bail if darcs version is too old

Merge with crew-stable

gendoc: don't translate topic strings twice (issue1760)

dirstate: fold paths using the just added util.realpath() function. Using the one true canonical path of a directory entry allows equivalent paths to be treated gracefully. Equivalent means, in this case, differing directory entries resulting in the same, unique file system link to a file.

util: add realpath() for getting the 'true' path. The function is implemented for Mac OS X using the F_GETPATH fcntl, and a basic implementation for Windows is provided as well. On other POSIX systems, vanilla os.path.realpath() is used.