Subclass pkginfo's Installed class to find metadata

When a package is installed as a wheel, pkginfo cannot properly find its
metadata. To resolve this, a patch has been posted to
https://bugs.launchpad.net/pkginfo/+bug/1437570 and those fixes have been
included here.

This silences UserWarnings from pkginfo about not being able to find
PKG-INFO for a package and allows twine to accurately report pkginfo's
version once installed.

Closes pypa#114

twine/_installed.py

@@ -0,0 +1,58 @@
+# Copyright 2013 Tres Seaver
+# Copyright 2015 Ian Cordasco
+# This code was originally licensed under the Python Software Foudation
+# License by Tres Seaver. In order to facilitate finding the metadata of
+# installed packages, part of the most current implementation of the
+# pkginfo.Installed class is reproduced here with bug fixes from
+# https://bugs.launchpad.net/pkginfo/+bug/1437570.
+import glob
+import os
+import sys
+import warnings
+
+import pkginfo
+
+
+class Installed(pkginfo.Installed):
+
+    def read(self):
+        opj = os.path.join
+        if self.package is not None:
+            package = self.package.__package__
+            if package is None:
+                package = self.package.__name__
+            egg_pattern = '%s*.egg-info' % package
+            dist_pattern = '%s*.dist-info' % package
+            file = getattr(self.package, '__file__', None)
+            if file is not None:
+                candidates = []
+
+                def _add_candidate(where):
+                    candidates.extend(glob.glob(where))
+
+                for entry in sys.path:
+                    if file.startswith(entry):
+                        _add_candidate(opj(entry, 'METADATA'))  # egg?
+                        _add_candidate(opj(entry, 'EGG-INFO'))  # egg?
+                        # dist-installed?
+                        _add_candidate(opj(entry, egg_pattern))
+                        _add_candidate(opj(entry, dist_pattern))
+                dir, name = os.path.split(self.package.__file__)
+                _add_candidate(opj(dir, egg_pattern))
+                _add_candidate(opj(dir, dist_pattern))
+                _add_candidate(opj(dir, '..', egg_pattern))
+                _add_candidate(opj(dir, '..', dist_pattern))
+
+                for candidate in candidates:
+                    if os.path.isdir(candidate):
+                        path = opj(candidate, 'PKG-INFO')
+                        if not os.path.exists(path):
+                            path = opj(candidate, 'METADATA')
+                    else:
+                        path = candidate
+                    if os.path.exists(path):
+                        with open(path) as f:
+                            return f.read()
+
+        warnings.warn('No PKG-INFO or METADATA found for package: %s' %
+                      self.package_name)

twine/cli.py

@@ -22,6 +22,7 @@
 import pkginfo
 
 import twine
+from twine._installed import Installed
 
 
 def _registered_commands(group='twine.registered_commands'):
@@ -31,7 +32,7 @@ def _registered_commands(group='twine.registered_commands'):
 
 def dep_versions():
     return 'pkginfo: {0}, requests: {1}, setuptools: {2}'.format(
-        pkginfo.Installed(pkginfo).version,
+        Installed(pkginfo).version,
         # __version__ is always defined but requests does not always have
         # PKG-INFO to read from
         requests.__version__,