Change pg_cancel_*() to ignore current backend

I find it annoying to have to specifically exclude pg_backend_pid() from 
pg_stat_activity if I'm trying to kill a bunch of backends at once, and 
I can't think of any reason why you'd ever want to call a pg_cancel_* 
function with your own PID.

Any objections to modifying those functions so they do nothing when 
handed the PID of the current backend?
-- 
Jim Nasby, Data Architect, Blue Treble Consulting
Data in Trouble? Get it in Treble! http://BlueTreble.com