Code review for dtrace probes added (so far) to 8.4. Adjust placement of

Code review for dtrace probes added (so far) to 8.4.  Adjust placement of
some bufmgr probes, take out redundant and memory-leak-inducing path arguments
to smgr__md__read__done and smgr__md__write__done, fix bogus attempt to
recalculate space used in sort__done, clean up formatting in places where
I'm not sure pgindent will do a nice job by itself.