Testing infrastructure: mocktime fixes

[gavinandresen]

New, undocumented-on-purpose -mocktime=timestamp command-line
argument to startup with mocktime set. Needed because
time-related blockchain sanity checks are done on startup, before a
test has a chance to make a setmocktime RPC call.

And changed the setmocktime RPC call so calling it will not result in
currently connected peers being disconnected due to inactivity timeouts.

[laanwj]

utACK

[paveljanik]

RPC call setmocktime checks for regtest network, but SetMockTime does not contain such check. When the user adds this argument on !regtest network, mocktime is thus set. Do you want it this way as this is a change to the current status quo where user is not allowed to set mocktime on !regtest networks?

[laanwj]

@paveljanik Good catch! (though I have no opinion on whether this is a problem - we don't advertise the parameter anyhow)

[paveljanik]

I do not have a problem with this too.
ACK