Add frequency count to extra::stat. #8281
auto merge of #8320 : mihneadb/rust/freq_count, r=cmr
std::rt: 2MB stacks again
std::rt: Pull RUST_MIN_STACK from the environment
std: Allow spawners to specify stack size
rustc: Use 4MB stacks. Needed for unoptimized builds apparently.
rustpkg: Disable test_uninstall

Seems to not work
test: xfail a bunch of tests that are incorrectly reading os::args()[1]
test: Fix deadlock in task-perf-linked-failure
xfail debug-info/option-like-enum

Don't understand why this broke.
doc: Fix deadlocks in tutorial due to yield bustage
Disable linked failure tests

The implementation currently contains a race that leads to segfaults.
rusti: Disable tests

Segfaulted on one of the bots. Maybe out of stack?
Turn on the new runtime
auto merge of #8358 : brson/rust/newrt, r=brson
Enabled workstealing in the scheduler. Previously we had one global work queue shared by each scheduler. Now there is a separate work queue for each scheduler, and work is "stolen" from other queues when it is exhausted locally.
It turns out that using rng() naively creates one that goes through urandom. This is really really bad as the random approach in the stealing loop. A very simple approach is now implemented that uses a basic psudorandom technique and maintains state in the scheduler struct.
changes to the random implementation used for scheduling and also changes to how bench tests are structured