This is the new way to refer to tasks in rust-land. Currently all they
do is serve as a key to look up the old rust_task structure. Ideally
they won't be ref counted, but baby steps.

Add new arg-passing mode 'move' denoted with '-T'. Translate as pass-by-value, doesn't deinit source yet nor get proper analysis in typestate, alias passes.

channel lifecycle bugs.

Added an unsafe way to pass libchans over spawn and chans, and converted task-comm-0 to use libcomm.

Needs to run on loopback so it doesn't trigger windows firewall, but seems
to be hanging. Giving up for now.

This causes trouble in Valgrind in drop glue in parsing.

This reverts commit 4d180793.

Previously, typestate was initializing the init constraint for
a declared-but-not-initialized variable (like x in "let x;") to False,
but other constraints to Don't-know. This led to over-lenient results
when a variable was used before declaration (see the included test
case). Now, everything gets initialized to False in the prestate/poststate-
finding phase, and Don't-know should only be used in pre/postconditions.

This aspect of the algorithm really needs formalization (just on paper),
but for now, this closes #700

Seem to work consistently