Merged from trunk 5196:5205

Merged from trunk 5196:5205

For bug #157385, enable portage.digestgen() to fetch any distfiles for
which there are no existing digests.

Fix broken SRC_URI logic from the previous commit.

Fix broken SRC_URI logic in doebuild.

Make repoman bail out if it's unable to generate the Manifest.

For bug #157393, fix up ebuild path normalization so that it's
compatible with portdbapi handling and works properly with symlinks
(like crossdev creates).

Make sure the ebuild path is properly normalized.

Revert r5175 for bug #152127 since the original = behavior seems more
desirable.  We can change the >= and <= behavior instead.

For bug #152127, make vercmp give less value to implcit .0, so two
versions that aren't literally equal are not ambiguously given the same
value (in sorting, for example).

svn path=/main/branches/prefix/; revision=5224