Use correct integer division

Without this, we get the following on Python 3:

    return '%s%*s' % (markup_fn(text), pad_len, '')
    TypeError: * wants int

WTF? docutils does not set up dependency correctly?  Or pip does not
handle it??

Python 3.4

Python 2.5 is not listed as supported version, according to
http://about.travis-ci.org/docs/user/languages/python/

Respect the `LESS' environment variable.

Steal a few more lines from git's pager code and only pass the hardcoded
"-FRSX" flags if the user has not set the LESS environmen variable to some
other variable, thus behaving more closely to what the user would expect.

Remove obsolete code

Handle Latin-1 encoded text in diffs

This is useful for avoiding crashing on "cdiff -l" (on Python 3) in
https://github.com/myint/cppclean.

Also handle unknown encodings gracefully rather than crashing.

Have to create pager Popen object before the translator Popen object
in PatchStreamForwarder, otherwise the `stdin=subprocess.PIPE` would cause
trouble to the translator pipe (select() never see EOF after input stream
ended), most likely python bug 12607 (http://bugs.python.org/issue12607)
which was fixed in python 2.7.3.

blocking mode with select() and bufsize=1, buggy in python 2.x:
close() does not notify select() for EOF

Remove code made unnecessary by #28

Also handle abruptly closed pipe gracefully.

Use OptionGroup for hack

- Close issue #26 (user can now use cdiff -s -U5 --cached)