Moving pg_autovacuum from contrib to src/bin

Having no response from my email to hackers yesterday, I will assume
(hope) that no news is good news and proceed onwards.

As outlined in my email, step 1 is to move pg_autovacuum from contrib to
src/bin.  Attached is a patch that modifies src/bin/Makefile and the
pg_autovacuum Makefile which will be in src/bin/pg_autovacuum/Makefile
once the pg_autovacuum directory is moved.

If there is anything else I can to to facilitate this move, let me know
and I'll do it.

Matthew O'Connor