Select latest version of package (if it is not pinned), and print
error if it cannot be installed due to other dependencies.
Together with --available, it selects the latest package which is
present at least in some repository.
This also fixes few solver issues with ordering of package selection
that got quite apparent with this flag. Namely, we cannot "lock"
a package until it's reverse dependencies are locked or not all of
the solver flags are propagated properly.
Instead of the dependency oriented logic, switch to print them
for each package or name needed. Might give a bit more readable
errors now. There's still few corner cases that proper error is
not output, which are cought by the test cases.
* the solver no longer does look-ahead locking of names
(could be possibly optimized later); instead names are now
always ordered strictly to properly detect the package names
which are unsolveable
* basic error tests added, so we can see the most likely problem
in dependencies easily
Timo Teräs