Expose a static helper function in libsvn_subr/path.c as a public API.

Copies of this function exist in libsvn_fs_fs and libsvn_repos, and
subsequent commits will remove this code duplication. I'm committing this
change in isolation to simplify potential future merges to 1.8.x/1.7.x.

* subversion/include/svn_path.h
  (svn_path_illegal_path_escape): Declare.

* subversion/libsvn_subr/path.c
  (illegal_path_escape): Rename to ...
  (svn_path_illegal_path_escape): ... this. Docstring has been moved to
   the public header. Otherwise unchanged.
  (svn_path_check_valid): Update caller.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1481625 13f79535-47bb-0310-9956-ffa450edef68
* subversion/libsvn_fs_fs/tree.c
  (escape_newline): Remove.
  (check_newline): Update caller, use svn_path_illegal_path_escape() instead.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1481627 13f79535-47bb-0310-9956-ffa450edef68
* subversion/libsvn_repos/commit.c
  (illegal_path_escape): Remove.
  (check_valid_path): Update caller, use svn_path_illegal_path_escape() instead.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1481628 13f79535-47bb-0310-9956-ffa450edef68
Remove duplicated docstring.

* subversion/libsvn_subr/path.c
  (svn_path_illegal_path_escape): As above.  Duplicate is at the declaration.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1481629 13f79535-47bb-0310-9956-ffa450edef68
* subversion/libsvn_subr/path.c
  (svn_path_illegal_path_escape): Fix an off-by-one allocation.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1481631 13f79535-47bb-0310-9956-ffa450edef68