Improve the Pipeline detection in Allocator.

Prior to this patch Allocator::ActivateThreads would use
RTTY on the currently active process to determine whether
the method is called indirectly from Pipeline::DoPipeline.

This patch creates a dedicated status bit in Pipeline
to report the same information. This drops the only
remaining dependency on Process::GetObject().
Improve the implementation of Simulator::delegate.

This patch generalizes Simulator::delegate into
Simulator::delegate_gen, to enable its reuse for other
callback signatures. This uses the new variadic template
syntax introduced in C++11. The special case is
still typedef'ed to "delegate" for convenience.

The "GetObject" service is removed, as it is not used
any more in MGSim.
Kill a compiler warning about a shadowed definition.