Allow the parser to understand upper and lower case letters.

We should pass bad commands onto git to get the standard
"git: 'X' is not a git command. See 'git --help'." message.

==========

Interestingly, git blows up if you hand it real commands with uppercases in them:
```
$ git A
git: 'A' is not a git command. See 'git --help'.

Did you mean one of these?
	am
	co
	gc
	mv
	p4
	rm
	st

$ git ADD
fatal: cannot handle ADD internally
```