pgsql: Move build of src/backend/replication/walreceiver/ later in the

Log Message:
-----------
Move build of src/backend/replication/walreceiver/ later in the build
process, after src/interfaces, because it depends on libpq. Also add
missing lines for clean etc. targets

Report from Boszormenyi Zoltan.

Modified Files:
--------------
    pgsql/src:
        Makefile (r1.48 -> r1.49)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/Makefile?r1=1.48&r2=1.49)