misc: Fix a number of unitialised variables and members

Static analysis unearther a bunch of uninitialised variables and
members, and this patch addresses the problem. In all cases these
omissions seem benign in the end, but at least fixing them means less
false positives next time round.
sim: Fix resource leak in BaseGlobalEvent

Static analysis revealed that BaseGlobalEvent::barrier was never
deallocated. This changeset solves this leak by making the barrier
allocation a part of the BaseGlobalEvent instead of storing a pointer
to a separate heap-allocated barrier.
mem: Add accessor function for vaddr

Determine if a request has an associated virtual address.
cpu: Only iterate over possible threads on the o3 cpu

Some places in O3 always iterated over "Impl::MaxThreads" even if a CPU had
fewer threads.  This removes a few of those instances.
config: Fix vectorparam command line parsing

Parsing vectorparams from the command was slightly broken
in that it wouldn't accept the input that the help message
provided to the user and it didn't do the conversion
on the second code path used to convert the string input
to the actual internal representation.  This patch fixes these bugs.
sim: Automatically unregister probe listeners

The ProbeListener base class automatically registers itself with a
probe manager. Currently, the class does not unregister a itself when
it is destroyed, which makes removing probes listeners somewhat
cumbersome. This patch adds an automatic call to
manager->removeListener in the ProbeListener destructor, which solves
the problem.