r2180: added RPC flags "padcheck" which enables checking of all received pad

r2180: added RPC flags "padcheck" which enables checking of all received pad
bytes to make sure they are zero. Non-zero values usually indicate one
of two things:

 - the server is leaking data through sending uninitialised memory
 - we have mistaken a real field in the IDL for padding

to differentiate between the two you really need to run with
"print,padcheck" and look carefully at whether the non-zero pad bytes
are random or appear to be deliberate.
(This used to be commit 7fdb778f81f14aaab75ab204431e4342a462957a)