Regenerate the amq RPC stubs with a -current rpcgen, with some

Regenerate the amq RPC stubs with a -current rpcgen, with some
post-processing of the server stub to match previous local changes.
This corrects the type handling of mt_mounttime, so "amq /mountpoint"
doesn't segv trying to treat a time_t as a pointer.
With the file (re)generation fixed, we can more easily update the
protocol to support 64bit time_t...