Sets Content-Type header based on headers and/or self.binary.mimetype values
		Implicitly favors Content-Type header if set

		Args:
			None

		Returns:
			None: sets attributes in self.binary and headers

def _prep_binary_mimetype(self):

		'''
		Sets Content-Type header based on headers and/or self.binary.mimetype values
		Implicitly favors Content-Type header if set

		Args:
			None

		Returns:
			None: sets attributes in self.binary and headers
		'''

		# neither present
		if not self.mimetype and 'Content-Type' not in self.resource.headers.keys():
			raise Exception('to create/update NonRDFSource, mimetype or Content-Type header is required')

		# mimetype, no Content-Type
		elif self.mimetype and 'Content-Type' not in self.resource.headers.keys():
			logger.debug('setting Content-Type header with provided mimetype: %s'
				% self.mimetype)
			self.resource.headers['Content-Type'] = self.mimetype