Created Unassigned: [0.3.x] some functions disturb thread context [13725]

see discussion: https://pykd.codeplex.com/discussions/645468

repro steps:

```
0:000> .load pykd
0:000> !py
Python 2.7.9 (default, Dec 10 2014, 12:28:03) [MSC v.1500 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> import pykd
>>> pykd.dbgCommand('r rax=1')
>>> pykd.getProcessSystemID()
2284
>>> pykd.dbgCommand('r rax=1')
Traceback (most recent call last):
File "<console>", line 1, in <module>
DbgException: Call IDebugControl::ExecuteWide failed
HRESULT 0x80040205
>>> quit()
0:000> r rax=1
Last set context:
^ Bad register error in 'r rax=1'

```