Various fixes for gh clone

[tgkokk]

1. When you run gh clone git://github.com/jingweno/gh gh, gh would transform it into git clone git://github.com/jingweno/gh git://github.com/tgkokk/gh. In other words, it wouldn't stop if it found a URL. I fixed it.
2. I added noop. (not really a fix)
3. Now, if gh clone foo bar is run, git clone git@github.com:tgkokk/foo bar is run. It's what hub also does, you can check with hub --noop.

[owenthereal]

good findings! Merged with minor fixes: 5351ec4

[tgkokk]

Thanks. Don't merge #71 yet, I will apply the fix about stopping to it too.