Added handling for the colon character

It is common to group commands into namespaces by using a colon in the command name to separate them.
However standard bash completion treats the colon as a wordbreak (useful for ssh/scp)
This change allows bash completion to work with commands including a colon character
Based on the answer from this stack overflow quetion:
http://stackoverflow.com/questions/10528695/how-to-reset-comp-wordbreaks-without-effecting-other-completion-script