validate multi-sig address

This is a test I have been using to validate a 2-of-3 multi sig address
using known public keys as well as validating the multi sig address
from the redeem script. I am working on more redeem script validation
tests but I want to make sure I am on the right track and see if this
test is something you all would deem useful.
Merge pull request #95 from juliustayl/multisig-tests

validate multi-sig address