better errors for import libusgscsm

from csmapi import csmapi

# Register the usgscam plugin with the csmapi

libusgscsm_path = find_library('usgscsm')

lib = ctypes.CDLL(find_library('usgscsm'))

if not lib:

if not libusgscsm_path:

    warnings.warn('libusgscsm not installed, unable to load shared library.')

libusgscsm = ctypes.CDLL(libusgscsm_path)

if not libusgscsm._name:

    warnings.warn('Unable to load usgscsm shared library')