subdirectories of pkgsrc/mk. Move the following files around for
locality:
pkgsrc/mk/scripts/extract -> pkgsrc/mk/extract/extract
pkgsrc/mk/bsd.sites.mk -> pkgsrc/mk/fetch/sites.mk
Also get rid of the recursive make for the "fetch" and "extract"
targets. This basically merges the "fetch" and "extract" phases into
the "patch" phase.
There is still much more work to do to simplify the fetch code, but
this is a good start.
