Revision 1037662

Introduce an svn_fspath__* API for manipulating Subversion filesystem paths
that start with a '/'.  Presently, the svn_uri_* API is being abused for
this purpose; once the callers all use svn_fspath__*, the svn_uri_* API can
be tightened up.  The functions provided initially are just those that that
are currently needed in libsvn_fs*, libsvn_repos and libsvn_ra*.

If FSPATH_USE_URI is defined during compilation, the implementation forwards
to the svn_uri_* API, which could be helpful in tracking down any problems
or differences that may be encountered while porting the callers.

* subversion/include/svn_dirent_uri.h,
  subversion/libsvn_subr/dirent_uri.c
  (svn_fspath__is_canonical, svn_fspath__join, svn_fspath__is_child,
   svn_fspath__basename): New functions.

* subversion/tests/libsvn_subr/dirent_uri-test.c
  (test_fspath_is_canonical, test_fspath_join, test_fspath_is_child,
   test_fspath_basename): New tests.
  (test_funcs): Add the new tests.