Bash completion

This gets bash completion working automatically in my Ubuntu distribution and should - hopefully - be portable. I have removed the "have" command at the start of the file because I can't find a way to use it in my distribution and it just causes an error. The completion should work as soon as a new shell is opened.

It will need some assessment to see what happens on systems which do not have pkg-config or bash so it should be considered a work in progress.