Merged from trunk 4500:4514

Merged from trunk 4500:4514

try to give the emerge manpage a facelift, upgrade clean and prune docs, change
'dependency' to 'atom', other minor fixes (WarnerBro)

Use a pickle to cache vdb metadata.  This greatly improves the performance for
loading the vdb when the buffer cache is cold.

Make portdbapi.flush_cache() consistent with vardbapi.flush_cache().

Update emerge --metadata docs for more clarity.

Allow the list of keys cached by the vardb to change without forcing a cache
version bump.

Make vartree.getslot() use the dbapi for aux_get caching.

Make vardbapi.cpv_counter() use aux_get for caching.

For bug #159252, don't preserve file attributes when copying files for
installsources.  Thanks to Ed Catmur <ed@catmur.co.uk> for this patch.

For bug #159295 and python-2.3 compatibility, don't assume that dict.update can
use an iterable.

Use a pickle to cache blockers for all installed packages so that dep_check
doesn't have to be called for every single installed package on every invocation
of emerge.

For bug #159161, make emerge --info show USE_EXPAND flags similar to the way it
does in merge list output.

Add some docs for the blockers cache format.

For bug #159310, don't show a slot collision notice if there are unresolvable
blockers.

Do some minor cleanup in the dep_zapdeps downgrade avoidance logic (while
working toward a fix for bug #159360).

svn path=/main/branches/prefix/; revision=5426