fix default event port behavior along with FileDescriptorActivity

[doudou]

This is the rock-specific version of orocos-toolchain#320

For the rationale behind the existence of this fork, see rock-core/package_set#167

Depends on:

• switch to our fork of rtt package_set#167

With the introduction of the work() method, which allowed to
be more precise on what gets called in which condition,
an event port under FileDescriptorActivity would not make
updateHook get called anymore.

This broke the Rock workflow with file descriptor activities.
(Un)fortunately, the effect has been subtle enough to not be
noticed readily. Or people started deploying tasks under the
normal Activity where before it would work with the FDA (I'm
guilty of that).

This is a rather convoluted code path (the characters in the
play are a FileDescriptorActivity 'FDA', ExecutionEngine 'EE'
and a TaskContext 'TC'

• the port signal calls FDA::trigger()
• FDA::trigger() wakes-up the FDA loop, which calls EE::work(Trigger)
• EE::work(Trigger) calls EE::processPortCallbacks but NOT
  EE::processHooks (expected from the work() refactoring)

At that point, we have to remember that TC::addEventPort registers
a port callback that by default calls TC::trigger(). The
comment at that point in the code itself says "default schedules
an updateHook" (which we're indeed expecting with a FDA)

• so, EE::processPortCallbacks in the end calls TC::trigger
• which, by default calls FDA::timeout

And FDA::timeout() was not implemented.