Removes check for IP:port availability if using replace_address.

Normally you want ccm to warn you that an IP:port is already in use,
however if you are using replace_address it's assumed you know what
you're doing. If the IP:port is in use, you'll see a C* error rather
than a ccm error.
Merge pull request #95 from EnigmaCurry/replace_address_fixes

Removes check for IP:port availability if using replace_address.