Improve build process

[Emilien Klein]

When building the Debian package, the following message appears:

WARNING: the following files are not recognized by DistUtilsExtra.auto:
  CHANGELOG
  PKG-INFO
  doc/nautilus-image-manipulator.1
  po/nautilus-image-manipulator.pot

Ensure that this warning is not displayed.

Also, the current packaging places the Nautilus extension file both in the extensions folder (correct):
/usr/share/nautilus-python/extensions
But also along with the other source files (incorrect):
/usr/share/nautilus-image-manipulator/nautilus_image_manipulator/

The extension should not be present at both places. Suggestions:
- Remove the file from /usr/share/nautilus-image-manipulator/nautilus_image_manipulator/
- Leave the file there and symlink it from /usr/share/nautilus-python/extensions (instead of a hard copy)

[Emilien Klein (emilien-klein)]

r111 removes the manfile from the warning list

[Emilien Klein (emilien-klein)]

Make sure backup files are not included in the release tarball. For instance, 0.5 as the following file:
data/ui/NautilusImageManipulatorDialog.ui~