Add missed call to pkg_list_free for PKG_PROVIDES.
Add picosat code.
Integrate picosat to pkg.
More simple assignment.
Request are now SAT assumptions.
Print problematic assumptions if sat problem was not solved.
Some cleanup.
Do not guess assumptions.
Rework installation candidates checking.
Merge pull request #914 from vstakhov/picosat

Use picosat solver as SAT solver
Do not install unneeded stuff.
Remove dead code.
Print number of upgrade candidates.
Fix request addition.
Resolve UNSAT problems manually.
Fix issue with seen packages not added to the request.
Check repository and force update if it is not valid.
Add debugging for rules.
Remove dead code.
Use plain .so for all shared libraries for now.

Since shared library parsing is broken completely atm, introduce a hack
to use merely libname.so as requires/provides for pkg.