Implement negative refspecs in JGit fetch, following C Git. Git
supports negative refspecs in source only while this change supports
them in both source and destination.
If one branch is equal to any branch or matches any pattern in the
negative refspecs collection, the branch will not be fetched even if
it's in the toFetch collection.
With this feature, users can express more complex patterns during fetch.
Change-Id: Iaa1cd4de5c08c273e198b72e12e3dadae7be709f
Sign-off-by: Yunjie Li<yunjieli@google.com>
eca101fc05