change mask rebinning in `def fit`

		fit_points = fit_points.reshape((-1,self.ndims))

		# self.detector_mask = None

		# if self.detector_mask is None:

		# 	detector_mask = fit_data==fit_data

		if self.detector_mask is not None:

			detector_mask = rebin_histogram(self.detector_mask.astype(int), bins)>0

			fit_data   = fit_data[detector_mask.ravel()]

			fit_points = fit_points[detector_mask.ravel(),:]

			if np.any(np.array([len(b) for b in bins])!=self.shape):

				# all subbins must be in detector mask, 0.99 to account for numerical error

				mask = rebin_histogram(self.detector_mask.astype(float), bins, mode='density') > 0.99

			else:

				mask = self.detector_mask

			fit_data   = fit_data[mask.ravel()]

			fit_points = fit_points[mask.ravel(),:]

		###########################################################################

		# initialization and bounds on parameters