Ir iterator interproc

[ailrst]

(merged into staging)

Addresses #157 and #156 and #168

• Interprocedural iterators now return the fallthrough target for indirect calls, and for directcalls, and only returns the procedure when the target has an implementation.
• Adds fallthrough edge to blocks as an optional GoTo. This means it is now included in incomingJumps sets etc. It also means the reverse interprocedural iterator jumps to the called-procedure's return call from the aftercall goto.
• Distinct return blocks are added
• Defines extension methods for checking whether a cfgnode is a procedureEntry, procedureReturn, afterCall node.

The interface for checking is like this:

        b match {
          case b: GoTo if b.isAfterCall => ...
          case _                => ...
        }

[ailrst]

Bug; the aftercall flag is not updated when the indirect call is resolved so the pred() / reverse iterator visits the old indirect call that is detached from the IL.
fixed

[ailrst]

This is already part of staging