Show full log in Subversion

Without this, some of the logs will not be shown.

- Fixed a bug in diff format probe
- Handle keyboard interrupt and large diffs in non-color mode
- Code clean up

Handle keyboard interrupt gracefully

Previously, a keyboard interrupt would result in a corrupted terminal.
This would manifest when doing "cdiff --log" on somewhat large
repositories.

The user explicitly asked for a log and thus knows what he is doing.

This will use the patch log from git, svn, or hg.

Add Travis CI test configuration

This will run the tests on CPython (2.5-3.3) and PyPy. Each push will
automatically trigger a test run on the Travis CI server.