Uw multicall

[uwiger]

@SPEC multicall(Module::atom(), Func::atom(), Args::list()) ->
{[Result], [{node(), Error}]}

@doc Perform a multicall RPC on all live gproc nodes

This function works like {@link rpc:multicall/3}, except the calls are
routed via the gproc leader and its connected nodes - the same route as
for the data replication. This means that a multicall following a global
registration is guaranteed to follow the update on each gproc node.

The return value will be of the form {GoodResults, BadNodes}, where
BadNodes is a list of {Node, Error} for each node where the call
fails.
@EnD

[uwiger]

As with the previous PR, the Travis-CI failures seem to be unrelated to this change. The t_multicall/1 test case worked each time.