Get correct VCS URL from prospective VCS URLs

From discussion with @pombredanne we came to the conclusion that for matching source repo URL with a PURL when we have multiple prospective VCS URLs:
1st - Follow redirects
2nd - Exact match on name and namespace
3rd - Approximate match on name using diff-lib
4th - File similarities, by pair we want to compare the contents of the package that has a purl vs the git repo in question (package manifest or metadata)
Using deltacode to find similarities
Delegate whole matching to purldb, compute similarities
Last resort- D2D between the git source package and the binary package