Fixing VersionConflict and DistributionNotFound exceptions

These are due to packages being upgraded beyond what some depending package specifies (e.g. if you tend to do `pip list --outdated | xargs pip install --upgrade` or anything similar.)
To deal with this, we ignore version requirement if VersionConflict.

Not sure how we can end up in a DistributionNotFound scenario, but plenty of bug reports about it, so just ignoring those outright.

Fixes invl#7, invl#9, invl#10, invl#11.

pip_autoremove.py

@@ -3,7 +3,7 @@
 import optparse
 
 import pip
-from pkg_resources import working_set, get_distribution
+from pkg_resources import working_set, get_distribution, VersionConflict, DistributionNotFound
 
 
 __version__ = '0.9.0'
@@ -104,7 +104,18 @@ def get_graph():
 
 
 def requires(dist):
-    return map(get_distribution, dist.requires())
+    required = []
+    for pkg in dist.requires():
+        try:
+            required.append(get_distribution(pkg))
+        except VersionConflict as e:
+            print(e.report())
+            print("Redoing requirement with just package name...")
+            required.append(get_distribution(pkg.project_name))
+        except DistributionNotFound as e:
+            print(e.report())
+            print("Skipping %s", pkg.project_name)
+    return required
 
 
 def main(argv=None):