Merged from trunk 5427:5444

Merged from trunk 5427:5444

For bug #151326, prevent invalid comments from being returned by
portage.getmaskingreason().

Correct the package.mask lookup order in getmaskingreason().

For bug #141361, use an alarm signal to implement a 1 minute timeout for
processing inside an elog module.

Use a try/finally block to ensure that the alarm will always be
cancelled appropriately.

Use return values instead of direct sys.exit(123) calls when a merge
fails.

Send errors in elog_process() to stderr via writemsg.

For bug #159518, increase the "database is locked" timeout.

Use slot atom matching to simplify detection of downgrades relative to
installed packages.

For bug #159224, use separate xmatch caches for each value of
ACCEPT_KEYWORDS.

For bug #159638, fix the UnboundLocalError in vartree.getprovide().

Fix the writemsg noiselevel from the previous commit.

merge all of the QA related checks together (SpankMan)
(needed manual diff)

Don't bother to list the contents of directories before they are
unmerged since it triggers unnecessary stat calls.  Thanks to James
Cloos <cloos@jhcloos.com> for reporting.

Optimize dep_zapdeps to work without a vartree when called by repoman.

svn path=/main/branches/prefix/; revision=5445