Generate random BigUints and BigInts
test the correct function (oops)
Convert between BigInts and BigUints
Fix Acceptor iterator ending early if a connection attempt fails
Forgot to make accept() home for IO
Make I/O tests use run_in_mt_newsched_task to get more multi-threaded test coverage
Incorporate feedback from huonw

- use identifiers with underscores to avoid unused variable warning
- implement on R: Rng instead of on R: RngUtil
- bugfix: zero BigInts were being generated twice as often as any
  other number
- test that gen_biguint(0) always returns zero
Add with_mem_writer to std::rt::io::mem.

This is in many ways a replacement for the current
std::io::with_str_writer.
Update for_expr docs.
Fix pretty-printing of empty impl items
workcache: Add the ability to save and load the database...

...as well as the ability to discover inputs and outputs.
rustpkg: Use workcache

rustpkg now uses the workcache library to avoid recompilation.
Hooray!
extra: Address review comments from Jack
rustpkg: Address review comments from Jack
Add test for issue #8587, about calling nested functions of the same name
Convert between BigInts, BigUints, ints, and uints

Previously, conversion to ints, uints, and BigUints clamped the value
within the range of that datatype. With this commit, conversion
overflows fail the task. To handle overflows gracefully, use the new
to_*_opt() methods.
Merge RandBigUint and RandBigInt into single trait
Implement bitwise operations on BigUint
librustc: Port writeback to the new API.
auto merge of #9083 : dcrewi/rust/biguint-bit-ops, r=brson