TBR: i#2157 re-attach: add best-effort re-attach support

Commit log for first patchset:
---------------
i#2157 re-attach: add best-effort re-attach support

While there are many globals that are not reset, we take a best-effort
approach here and reset the ones that matter, allowing us to re-attach with
a memtrace client and static DR.

Portions of this were initially based on
https://codereview.appspot.com/13314047/ from Peter Goodman.

For DO_ONCE, an incremented counter is used.

For numerous other globals, at exit time if doing_detach is set we reset
them to NULL.

For locks, we simply reset count_times_acquired but leave the deleted field
as it does not matter much (part of the whole theme here: this may never be
rock-solid for unusual option combinations but our goal is supporting the
common case).

For drreg, with the new multi-init feature we have to zero the options at
exit time.

Adds several tests by adding loops around existing start/stop tests, but
stops short on burst_threads until i#2175 is fixed.
---------------

[bruening, 2017-02-14 03:23:53]

Committed as
https://github.com/DynamoRIO/dynamorio/commit/2dd9659475aef0db32440e1f6adb745...

Final commit log: 
---------------
i#2157 re-attach: add best-effort re-attach support

While there are many globals that are not reset, we take a best-effort
approach here and reset the ones that matter, allowing us to re-attach with
a memtrace client and static DR.

Portions of this were initially based on
https://codereview.appspot.com/13314047/ from Peter Goodman.

For DO_ONCE, an incremented counter is used.

For numerous other globals, at exit time if doing_detach is set we reset
them to NULL.

For locks, we simply reset count_times_acquired but leave the deleted field
as it does not matter much (part of the whole theme here: this may never be
rock-solid for unusual option combinations but our goal is supporting the
common case).

For drreg, with the new multi-init feature we have to zero the options at
exit time.

Adds several tests by adding loops around existing start/stop tests, but
stops short on burst_threads until i#2175 is fixed.

Review-URL: https://codereview.appspot.com/318520043
---------------