Restore previous initial guess set.
Rework DPLL algorithm.
Fix free of solver's tree.
Apply replacements for unknown packages early.

Now we change uid of unknown packages just prior to fetching. That
should improve user's experiences when performing a complex upgrade.
Fix ensure loaded for files and dirs.
Fix ensure_loaded return value for remote packages.
Perform integrity check early if all packages are downloaded.

If all packages are downloaded then just do integritycheck without
bothering a user with multiple queries.

Suggested by:	az
Check fetched only for remote packages.
Add PKG_OPEN_TRY flag to pkg_open.

Do not emit fatal message when it is impossible to load package if flag
PKG_OPEN_TRY has been specified.
Update to release candidate 2.