fixing cap_pvpapi interface

This PR tries to fix the following 3 reported issues
- http://code.opencv.org/issues/3946
- http://code.opencv.org/issues/3947
- http://code.opencv.org/issues/3948

Basically it enables use of monochrome AVT cameras AND lets the initialize wait long enough since newer cams have a longer initialization time!
The shold be PvCameraCount() or PvCameraList() both should work. However, it's cleaner to call PvCamaerCount() first in my mind.