pgsql: Separate out the VacRUsage stuff as an independent module, in

Log Message:
-----------
Separate out the VacRUsage stuff as an independent module, in preparation
for using it for other things besides VACUUM.

Modified Files:
--------------
pgsql/src/backend/commands:
vacuum.c (r1.315 -> r1.316)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/vacuum.c.diff?r1=1.315&r2=1.316)
vacuumlazy.c (r1.59 -> r1.60)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/vacuumlazy.c.diff?r1=1.59&r2=1.60)
pgsql/src/backend/utils/misc:
Makefile (r1.23 -> r1.24)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/Makefile.diff?r1=1.23&r2=1.24)
pgsql/src/include/commands:
vacuum.h (r1.60 -> r1.61)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/commands/vacuum.h.diff?r1=1.60&r2=1.61)

Added Files:
-----------
pgsql/src/backend/utils/misc:
pg_rusage.c (r1.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/pg_rusage.c?rev=1.1&content-type=text/x-cvsweb-markup)
pgsql/src/include/utils:
pg_rusage.h (r1.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/pg_rusage.h?rev=1.1&content-type=text/x-cvsweb-markup)