virtual memory not tracked

[convolvatron]

there are tens of little regions floating around, with no real guarantee that they are disjoint.

keep a global map of virtual allocations with some semantic annotations.

use this to generate a proper /proc/self/maps which pthreads is using to locate
the stack

can also add a debugging aid - what was this address mapped for

[convolvatron]

also see #16

[wjhun]

We are now tracking virtual memory allocations for the process address space.