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.