gnu: Add python2-pathlib2.

Adding only the Python 2 variant, since for Python 3 our minimum version
is 3.4 which already includes this package as part of the standard library.

gnu/packages/python.scm (python2-pathlib2): New variable.

gnu/packages/python.scm

@@ -8887,6 +8887,42 @@ (define-public python-pathlib
 (define-public python2-pathlib
   (package-with-python2 python-pathlib))
 
+(define-public python2-pathlib2
+  (package
+    (name "python2-pathlib2")
+    (version "2.1.0")
+    (source (origin
+              (method url-fetch)
+              (uri (pypi-uri "pathlib2" version))
+              (sha256
+               (base32
+                "0p050msg5c8d0kadv702jnfshaxrb0il765cpkgnhn6mq5hakcyy"))))
+    (build-system python-build-system)
+    (arguments
+     `(#:python ,python-2))
+    (native-inputs
+     `(("python2-setuptools" ,python2-setuptools)
+       ("python2-six" ,python2-six)))
+    (home-page "http://pypi.python.org/pypi/pathlib2/")
+    (synopsis "Object-oriented file system paths - backport of standard
+pathlib module")
+    (description "The goal of pathlib2 is to provide a backport of standard
+pathlib module which tracks the standard library module, so all the newest
+features of the standard pathlib can be used also on older Python versions.
+
+Pathlib offers a set of classes to handle file system paths.  It offers the
+following advantages over using string objects:
+
+@enumerate
+@item No more cumbersome use of os and os.path functions.  Everything can
+be done easily through operators, attribute accesses, and method calls.
+@item Embodies the semantics of different path types.  For example,
+comparing Windows paths ignores casing.
+@item Well-defined semantics, eliminating any inconsistencies or
+ambiguities (forward vs. backward slashes, etc.).
+@end enumerate")
+    (license license:expat)))
+
 (define-public python-jellyfish
   (package
     (name "python-jellyfish")