Improve `hub alias` support for csh and tcsh.

This adds tcsh as a supported shell, adds profile filenames for csh and tcsh (~/.cshrc and ~/.tcshrc
respectively), corrects the alias command for [t]csh to 'alias git hub', and the eval command for the
same to 'eval "`hub alias -s`" as [t]csh doesn't support $() notation.

The cucumber tests for alias have been updated, and seem(?) to pass.

Source for ~/.tcshrc and tcsh aliasing: [tcsh man page]
Source for ~/.cshrc and csh aliasing: [csh man page]

[tcsh man page]: http://linux.die.net/man/1/tcsh
[csh man page]: http://www.unix.com/man-page/opensolaris/1/csh/