Add a draft implementation of arbitrary CAN message frequency control.

This adds two new dependencies, emlist and emhashmap.
Bump to latest of emhashmap to fix tests.
Grab emhashmap's emlist dependency by updating submodules recursively.
Import emlist dependency as a submodule inside emhashmap.
Fix memory leaks in dynamic message tracking.
Fix use of an uninitialized value.
Patch up test suite for PIC32, compiling without c99.
Fix passthrough message handler's rate control after testing.
For runtime CAN msgs, default to sending changed values immediately.
Merge branch 'next' into message-rate-control
Use message-rate-control branch of openxc Python lib.
Add originating CAN bus to raw CAN message output.
Grab latest version of pip in bootstrap.
Update Python lib dependency to 'next' branch.