New path library for dttools.

Moves some old path specific functions from stringtools to the new
namespace. Some cleanup of old functions with tests. Also a new useful
path_absolute function.
Corrects path handling in Chirp.

Chirp now always operates from the root directory.
Fix some bugs with path handling.
Correct errors on Darwin.
Added cvmfs option try_local_filesystem.  This is now used in the default configuration to allow access to locally mounted repositories that are not configured for access via parrot's cvmfs client.
Merge pull request #180 from dcbradley/cvmfs-try-local-filesystem

Added cvmfs option try_local_filesystem.
Remove old code.

The code changed the url path to an absolute path. This is done in cfs_reinterpret.
Merge pull request #172 from batrick/chirp-path-bugfix

Chirp path bugfix
Added Python 3 support for work_queue library.
Accomodate older versions of Python 3.
Fixed Python 3 detection bug in configure script.
Organize/alphabetize headers. Remove some repeats.
alphabetize/simplify
whitespace
Merge #181.
Extract filename extension from path
find extension for more types of paths
vim file settings
Merge pull request #187 from rampantmonkey/path_extension

Extract filename extension from path
Fix some bugs caused by #172.