The old one was not getting freed, creating a memory leak every exec(),
which can get huge over time.
Plus, there was no need for a new stack.
And we couldn't just free the old one, since sys_execve() runs on the old stack...
This is a more appropriate name now that it does more stuff than allocate virtual memory.
To be fair, the name was a bit awkward anyway. Should have been UserVMAllocator I guess.
The self directory, and the active directory. The active directory is the one the thread is currently using,
and the self directory is the one the thread owns.
This lets us keep track of both, which fixes ext2 executables crashing the system.
This can cover the entire address space at once in a more memory-efficient way.
Stress-tested using 'base64 /bin/ls' which allocates enough contiguous
virtual memory to store the entirety of /bin/ls :)
A couple of bugs and fixes later, here we are!
