* Make portdbapi.aux_get() automatically pull pre-generated metadata

* Make portdbapi.aux_get() automatically pull pre-generated metadata
  directly from the metadata/cache/ directory when metadata-transfer
  is not enabled in FEATURES. This makes all cache modules behave
  similar to existing metadata_overlay module, except when
  FEATURES="metadata-transfer" has been explicitly enabled.

* Remove metadata-transfer from FEATURES in make.globals so that it's
  no longer enabled by default. Users will be happy about this since
  the "Updating Portage cache" part of emerge --sync can be more time
  consuming than the rsync run itself. It's also nicer when when using
  PORTDIR over nfs or bind mounted in a chroot since there's no need
  to run emerge --metadata.

* Update FEATURES="metadata-transfer" docs to warn users of the rsync
  tree to modify eclases in PORTDIR_OVERLAY if necessary instead of
  doing it directly in the rsync tree.

* Relevant updates to /etc/portage/modules docs.

(trunk r9930)

svn path=/main/branches/2.1.2/; revision=9931