[loggingTools] add Logger class with support for 'lastResort' stderr handler

Both _StderrHandler and Logger.callHandlers included here are taken from Python 3.5's
logging.py source.

I only set logging.lastResort if it's not already set (i.e. for Python < 3.2).

Lib/fontTools/misc/loggingTools.py

@@ -87,6 +87,58 @@ class LevelFormatter(logging.Formatter):
 		return super(LevelFormatter, self).format(record)
 
 
+class _StderrHandler(logging.StreamHandler):
+	""" This class is like a StreamHandler using sys.stderr, but always uses
+	whatever sys.stderr is currently set to rather than the value of
+	sys.stderr at handler construction time.
+	"""
+	def __init__(self, level=logging.NOTSET):
+		"""
+		Initialize the handler.
+		"""
+		logging.Handler.__init__(self, level)
+
+	@property
+	def stream(self):
+		return sys.stderr
+
+
+if not hasattr(logging, 'lastResort'):
+	# for Python pre-3.2, set a "last resort" handler used when clients don't
+	# explicitly configure logging
+	logging.lastResort = _StderrHandler(logging.WARNING)
+
+
+class Logger(logging.Logger):
+	""" Add support for 'lastResort' handler introduced in Python 3.2.
+	You can set logging.lastResort to None, if you wish to obtain the pre-3.2
+	behaviour. Also see:
+	https://docs.python.org/3.5/howto/logging.html#what-happens-if-no-configuration-is-provided
+	"""
+
+	def callHandlers(self, record):
+		# this is the same as Python 3.5's logging.Logger.callHandlers
+		c = self
+		found = 0
+		while c:
+			for hdlr in c.handlers:
+				found = found + 1
+				if record.levelno >= hdlr.level:
+					hdlr.handle(record)
+			if not c.propagate:
+				c = None  # break out
+			else:
+				c = c.parent
+		if (found == 0):
+			if logging.lastResort:
+				if record.levelno >= logging.lastResort.level:
+					logging.lastResort.handle(record)
+			elif logging.raiseExceptions and not self.manager.emittedNoHandlerWarning:
+				sys.stderr.write("No handlers could be found for logger"
+								 " \"%s\"\n" % self.name)
+				self.manager.emittedNoHandlerWarning = True
+
+
 def configLogger(**kwargs):
 	""" Do basic configuration for the logging system. This is more or less
 	the same as logging.basicConfig with some additional options and defaults.