Handle obsolete matches (more) correctly in rpmal

Handle obsolete matches (more) correctly in rpmal

- Similar to commit 9fb81eac0bcd239e46459f72916099f1adfc5cb9 but
  on the to-be-installed set: obsoletes should only be matched against
  package names, not any provide or file names. Hasn't really mattered
  previously due to the way its called, but since commit
  05487d9a3f763cfed5f5ca75b4fbadb62f38dfd6 I guess it started to matter.
  It's more correct this way anyhow, and should fix RhBug:810077.
- Since rpmal only knows about provides, we need to handle obsoletes
  as a special case and filter out matches on provide names different
  than the matching package name.
(cherry picked from commit 8106e7e89c3c673f8eb7d2ed5027e2ee9750e3b5)