When tagopt is set to '--tags', we should only take the default tags
refspec into account and ignore any configured ones.
Bring the code into compliance.
It used to be separate as an attempt to make the querying easier, but
it didn't work out that way, so put all the data together.
Add git_refspec_string() as well to get the original string, which is
now stored alongside the independent parts.
Introduce git_remote_{fetch,push}_refspecs() to get a list of refspecs
from the remote and rename the refspec-adding functions to a less
silly name.
Use this instead of the vector index hacks in the tests.
A remote can have a multitude of refspecs. Up to now our git_remote's
have supported a single one for each fetch and push out of simplicity
to get something working.
Let the remotes and internal code know about multiple remotes and get
the tests passing with them.
Instead of setting a refspec, the external users can clear all and add
refspecs. This should be enough for most uses, though we're still
missing a querying function.
