RepositoryInfo had two old flags for indicating support for features,
supports_changesets and supports_parent_diffs. Having these in
the RepositoryInfo class was weird, since we have a bunch of other
support flags that live on the SCMClient class. Whether a client
supports these isn't something that might change from repository to
repository, so these should live on the client too.
This change moves those flags over. Unfortunately, unlike a lot of the
recent cleanups, this isn't something that can be done in a soft
deprecation. It seems pretty unlikely that there are custom SCMClient
implementations floating around which use these, but just in case, if
they try to use it after upgrading to RBTools 3.0, it'll spit out a
useful error message telling them how to fix it.
