Allow page allocations to include guard pages

The PageAllocator is in principle capable of using guard pages. We can
expose that functionality to its clients.

Change-Id: I919f6f76310feb160d2b26ac1fc64db4e91804bb
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Add guard pages around JavaScript stack

Like this we avoid writing to random memory if the stack overflows.

Change-Id: I0e0962daae69904a9ce21b047f3d8c0811c1d09f
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Implement guard pages for windows page allocator

Change-Id: Ia54a259bbf05cca7dc1ed868a75931efa95851b3
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Remove guard pages option from uncommitted page reservations

It's only implemented for non-linux unix-like systems and it's quite
challenging to get it right everywhere else. So, instead of giving the
user the illusion that guard pages might be available we just drop
them.

Change-Id: I7ec74c84f6215f22bd10758728b18bbecc0adf59
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Comment parameters to PageAllocation::allocate()

Change-Id: I8966fbc5f89ce470a0a16fe29086fa6e13ef408e
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>