Fix for sigsegv stack overflow behavior

[horenmar]

Also stops Catch from assuming its the only signal user in the binary,
and makes it restore the signal handlers it has replaced. Same goes for
the signal stack.

The signal stack itself probably shouldn't be always reallocated for
fragmentation reasons, but that can be fixed later on.

[horenmar]

This takes unconditional dependency on C++11 (in the form of including <array> and <memory>), while catch tries for C++03 conformance. Going to fix this later tonight.

[krvajal]

@philsquared any updates on this??

[philsquared]

@krvajalmiguelangel - I started work on my own signals fixes before I saw @horenmar's PR - and have now covered half of it - will look at the stack overflow part soon.

[horenmar]

I cherry picked this into dev-signals branch, so the PR is obsolete.