Add compact manifest to a package.

+MANIFEST contains all files and directories of a package and it
thus may be too expensive to parse and unpack it when we only want
to check version or create repository. Hence, on pkg create add
+COMPACT_MANIFEST initially and use it for quick lookups.

Use +COMPACT_MANIFEST on pkg-repo command (may reduce execution time
by several times for large packages).

Fallback to +MANIFEST if +COMPACT_MANIFEST is absent.