Turn off jemalloc
test: xfail bench/task-perf-one-million. OOM on 32-bit linux w/o opts
replace #[inline(always)] with #[inline]. r=burningtree.
xfail std::num::complex::test_norm on x86, r=burningtree.
rusti: disable tests on 32bit mac. r=burningtree.
vec: remove each_const

An Iterator implementation can be made for &const [T] if it turns out
to be necessary for some use case.
vec: remove eachi

replaced by the `enumerate` method from std::iterator
vec: rm old_iter implementations, except BaseIter

The removed test for issue #2611 is well covered by the `std::iterator`
module itself.

This adds the `count` method to `IteratorUtil` to replace `EqIter`.