Fix #32: Require authentication for the clone command

This makes the error reported to the user to make a bit more sense (not
perfect, but better), so also improves the status of issue #31.
Add GMANE links to the README file
Fix #36: Don't requite hub.upstream config for clone

This config value is actually created by this command.
Fix #40: Add missing documentation for pull rebase --force
Fix #38: properly interpret the saved --edit-msg argument

The `is` operator compares "pointers" a la C, the regular `==` compare
operator must be used to compare the contents of the strings.
rebase: Improve warning message when not mergeable
rebase: Add --pause option to pause before pushing

This option is particularly useful for testing, as it pauses the
`pull rebase` command just after the actual rebase was successful, before
the rebased code is pushed and the issue is closed.

Closes #39.
Clean up pull rebase after it was paused

A bug in the pause logic prevented the environment to be cleaned up (the
temporary branch to be removed and changes unstashed) after a pull
rebase was paused.
Fix #29: `git hub pull checkout`
Fix #44: Make rebase --pause message more verbose

The --pause option is now mentioned in the message and "Use --continue
ONCE MORE when done" is used when the rebasing was interrupted before to
resolve conflicts.
Fix #45: Convert strings to local encoding before printing
Fix #33: Require -c when creating a RM from a headless checkout

Now calculating the head and references to push is much smarter, we
learned the difference between having only the hash of the head and
having a branch name too, so we can make better pushes and report better
errors when a needed branch name is missing.
Release v0.5rc1
Makefile: Simplify version parsing from debian/changelog
Fix #47: Don't prepend an extra 'v' to the version
Makefile: Use git describe to set the man page version
Improve error reporting for unexpected HTTP errors

This was discovered by Ronnie Ridpath while helping to add support for
GitHub Enterprise:
http://librelist.com/browser//git.hub/2013/11/1/how-to-setup-with-github-enterprise/#4d0c4ad124b6f94b787aa2bead13c21e

When receiving a 404, the setup command didn't show any kind of error
output, because no GitHub error message was found in the reply body.
Release v0.5rc2
Fix #52: Use debian version when not in a git repo

When building the man, we need to get the current program version. As
long as the precise git version can be used, is the best way to go, but
if a tarball was downloaded instead of getting the program from the git
repository, we fall back to the debian version.
Fix 'git hub pull checkout' typo