BF: Use xlib in iohub on Linux.

Discussed on the old mailing list (https://groups.google.com/forum/#!topic/psychopy-dev/LUna_gm5YG4) but not committed.

Re-encountered recently at https://discourse.psychopy.org/t/issue-with-iohub-on-linux/2741

psychopy/iohub/devices/mouse/linux2.py

@@ -9,6 +9,7 @@
from . import MouseDevice
from ... import print2err,MouseConstants,printExceptionDetailsToStdErr
from .. import Computer,Keyboard
from .. import xlib

currentSec=Computer.getTime

@@ -33,8 +34,8 @@ def __init__(self,*args,**kwargs):
        if Mouse._xdll is None:
            try:
                Mouse._xdll = cdll.LoadLibrary('libX11.so') 
                Mouse._xdisplay = self._xdll.XOpenDisplay(None) 
                Mouse._xscreen_count = self._xdll.XScreenCount(self._xdisplay)  
                Mouse._xdisplay = xlib.XOpenDisplay(None) 
                Mouse._xscreen_count = xlib.XScreenCount(self._xdisplay)  
                try:
                    # should use linux cmd:
                    # find /usr/lib -name libXfixes.so\*