Added a trusted-plugin system

Summary:
A system for specifying plugins which do not get copied versions of the references passed to the plugin in params.

If plugins are loaded with --trusted-plugins then the references are not copied and any exceptions generated by the plugin will not be caught by the plugin manager.

Plugins loaded with --plugins now have extra seperation from arcyd.

Test Plan: Working on it

Reviewers: jevripio, phab

Reviewed By: jevripio

CC: phab

Differential Revision: https://sibld.phab.dev.bloomberg.com/D169
Arcyd: fix: replace bad unicode chars in diffs

In the event of bad unicode characters, replace them silently.  Later we
will want to report that we replaced them and provide some diagnostic of
where they were replaced.

Test Plan: $ ./precommit.sh
Arcyd: doc: add bad commit message concern
Arcyd: pep8: rawDiff -> raw_diff

Test Plan: $ ./precommit.sh
Arcyd: test get commit message after abandon/close

Test Plan: $ PYTHONPATH=py/phl nosetests py/abd/abdt_conduit__t.py
autofix: group imports by level and sort

To make imports easier to parse, in addition to sorting them also group
them by level, with lowest-level first.

Test Plan: $ ./precommmit.sh and inspect
autofix: insert selected 'from __future__' imports

To make the port to Python 3 a bit easier, add support for automatically
inserting future import statements in all library files.

This also adds support for such statements generally to the import
sorter, previously it would raise if it encountered such a statement.

Don't enforce any future imports in this commit.

Test Plan:
test inserting 'from __future__ import absolute_import'
$ ./precommit
Enhanced tracebacks, with local variables

Add a new component, phlsys_traceback which has support for printing
enhanced tracebacks with more information for debugging purposes.

Test Plan:
$ ./precommit.sh

Try installing the exception handler in various existing apps to see
that the output is as expected.  Some of the traces are a little
strange, possibly owing to outputting the contents of local variables.
Nothing appears to be actually wrong however.
Arcyd: install enhanced tracebacks

Install the new enchanced tracebacks to sys.excepthook and when mailing
exceptions around.

Be conservative and send two mails, the first with the regular message
and the second with the enhanced message; as the mechanism is currently
considered to be experimental.

Test Plan:
$ ./precommit.sh
WIP: abdweb