This update for libsolv fixes the following issues:

- some metadata may have caused a segfault (boo#980901)
- ignoreinst logic caused issues upgrading some Perl packages (boo#983141)

The new version is 0.6.21, which contains the following changes:

- add pool->setdisttype to the bindings
- fix error in repo_deb that could lead to missing packages
- add reason testing to testcase code
- add pool_whatcontainsdep, selection_make_matchdepid, and SELECTION_MATCH_DEPSTR
- add SOLVER_FAVOR and SOLVER_DISFAVOR job types
- allow unknown archs in pool_setarch
- add the SOLVER_FLAG_URPM_REORDER solver flag
- fix supplements handling when implicitobsoleteusescolors is set