Give to/from_x86 helpers external linkage to try to fix travis-ci/gcc 4.6
When XSAVE(64) is not available, fall back to GETFPXREGS on x86-32 and GETFPREGS on x86-64. Should fix Westmere.

Resolves #1392
Ignore (untracked) growth of the [stack] segment when asserting that our cached view of the address space matches the kernel's.
Account for a program break that may not be contiguous with the other executable image mappings.
Add gdb 'when' command to report current event number.

Resolves #1393.
Avoid using gcc initializer syntax in C++ ... trying to fix Travis
Get rr to build on fedora 21.