fix various bugs found by the 'prospector' static-analysis tool

gpiozero/pins/rpio.py

@@ -7,8 +7,6 @@ from __future__ import (
 str = type('')
 
 
-from threading import Lock
-
 import RPIO
 import RPIO.PWM
 from RPIO.Exceptions import InvalidChannelException
@@ -21,6 +19,8 @@ from ..exc import (
     PinFixedPull,
     PinInvalidPull,
     PinInvalidBounce,
+    PinInvalidState,
+    PinPWMError,
     )
 
 
@@ -126,7 +126,7 @@ class RPIOPin(Pin):
 
     def _set_state(self, value):
         if not 0 <= value <= 1:
-            raise PinInvalidValue('invalid state "%s" for pin %r' % (value, self))
+            raise PinInvalidState('invalid state "%s" for pin %r' % (value, self))
         if self._pwm:
             RPIO.PWM.clear_channel_gpio(0, self._number)
             if value == 0: