pgsql: Allow an autovacuum worker to be interrupted automatically when

Log Message:
-----------
Allow an autovacuum worker to be interrupted automatically when it is found
to be locking another process (except when it's working to prevent Xid
wraparound problems).

Modified Files:
--------------
    pgsql/src/backend/postmaster:
        autovacuum.c (r1.65 -> r1.66)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/autovacuum.c?r1=1.65&r2=1.66)
    pgsql/src/backend/storage/lmgr:
        README (r1.21 -> r1.22)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/lmgr/README?r1=1.21&r2=1.22)
        deadlock.c (r1.48 -> r1.49)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/lmgr/deadlock.c?r1=1.48&r2=1.49)
        proc.c (r1.195 -> r1.196)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/lmgr/proc.c?r1=1.195&r2=1.196)
    pgsql/src/include/storage:
        lock.h (r1.107 -> r1.108)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/lock.h?r1=1.107&r2=1.108)