Probably the env var should be renamed from DETAILED_LEAKS but I'm leaving
aside that breaking change for now.

I am going to use memory_region and boxed_region as the local heap
in the new scheduler, for now at least, and I don't have a rust_env
available.

it doesn't actually call calloc, so it's fairly pointless

Many changes to code structure are included:
- removed TIME_SLICE_IN_MS
- removed sychronized_indexed_list
- removed region_owned
- kernel_owned move to kernel.h, task_owned moved to task.h
- global configs moved to rust_globals.h
- changed #pragma once to standard guard in rust_upcall.h
- got rid of memory.h

this will be used to generate a new snapshot.

snapshot is prepared.

Happy to close the loop on this one.

Issue #236

We're trying to get closer to doing correct move semantics for channel
operations. This involves a lot of cleanup (such as removing the
unused sched parameter from rust_vec constructor) and making
circular_buffer kernel_owned.

Added tagging for memory allocations. This means we give a string tag
to everything we allocate. If we leak something and TRACK_ALLOCATIONS
is enabled, then it's much easier now to tell exactly what is leaking.

This is just until unwinding works. Adds a flag to the runtime to turn
the memory leak checks on task destruction into warnings instead of fatal
errors. I am so sorry.

Issue #428

Ports and channels have been moved to the kernel pool, since they've
been known to outlive their associated task. This probably isn't the
right thing to do, the life cycle needs fixed instead.

Some refactorying in memory_region.cpp. Added a helper function to
increment and decrement the allocation counter. This makes it easier
to switch between atomic and non-atomic increments. Using atomic
increments for now, although this still does not fix the problem.

Tidy up the sync dir, remove dead or mis-designed code in favour of OS primitives, switch rust_kernel to use a lock/signal pair and wait rather than spin.

Lots of changes around memory managment in the Runtime. Added memory regions and fixed race caused by calling rust_srv::malloc() from multiple threads when sending messages.