Use sync.c for upgrade transaction prepare and commit

Use sync.c for upgrade transaction prepare and commit

This patch utilizes the power of sync.c to fix FS#3492 and FS#5798.
Now an upgrade transaction is just a sync transaction internally (in alpm),
so all sync features are available with -U as well:
* conflict resolving
* sync dependencies from sync repos
* remove unresolvable targets

See http://www.archlinux.org/pipermail/pacman-dev/2009-June/008725.html
for the concept.

We use "mixed" target list, where PKG_FROM_FILE origin indicates local
package file, PKG_FROM_CACHE indicates sync package. The front-end can add
only one type of packages (depending on transaction type) atm, but if alpm
resolves dependencies for -U, we may get a real mixed trans->packages list.

_alpm_pkg_free_trans() was modified so that it can handle both target types
_alpm_add_prepare() was removed, we use _alpm_sync_prepare() instead
_alpm_add_commit() was renamed to _alpm_upgrade_targets()

sync.c (and deps.c) was modified slightly to handle mixed target lists,
the modifications are straightforward. There is one notable change here: We
don't create new upgrade trans in sync.c, we replace the pkgcache entries
with the loaded package files in the target list (this is a bit hackish) and
call _alpm_upgrade_targets(). This implies a TODO (pkg->origin_data.db is
not accessible anymore), but it doesn't hurt anything with pacman front-end,
so it will be fixed later (otherwise this patch would be huge).

I updated the documentation of -U and I added a new pactest, upgrade090.py,
to test the syncdeps feature of -U.

Signed-off-by: Nagy Gabor <ngaba@bibl.u-szeged.hu>
Signed-off-by: Dan McGee <dan@archlinux.org>