checkpoint this work, confirmed parsing CRW and CR2 files...

This still needs some cleanup and additional tests..  This isn't
hooked into the testing system yet as I still haven't decided if
I'm going to commit fixtures or not (or maybe make this it's own
repo)..

IFD needs serious cleanup.. I should be using a classmethod instead
of the janky nextptr bs.

ui/medashare/metadata/BitField.py

@@ -0,0 +1,62 @@
+class BitFieldMetaClass:
+	def __init__(self, name, bases, dct):
+		for base in bases:
+			if base.__class__ is not BitFieldMetaClass:
+				raise TypeError('BitField base class must be bit field')
+		bases = filter(lambda x: x is not BitField, bases)
+		self.__name__ = name
+		self.__bases__ = bases
+		d = self.__dict = {}
+		for key, value in dct.items():
+			if key[:2] == '__':
+				continue
+			assert isinstance(value, int)
+			d[key] = value
+
+	def __call__(self, val):
+		return BitFieldInstance(self.__name__, self.__dict, val)
+
+class BitFieldInstance(object):
+	def __init__(self, name, d, v):
+		self.__bfname = name
+		self.__dict = d
+		self.__value = v
+
+	name = property(lambda x: x.__bfname)
+
+	def __int__(self):
+		return self.__value
+
+	def __getattr__(self, k):
+		if k[:19] == '_BitFieldInstance__':
+			return object.__getattr__(self, k)
+
+		try:
+			return bool(self.__value & 1 << (self.__dict[k]))
+		except KeyError:
+			raise AttributeError('no field named: %s' % repr(k))
+
+	def __setattr__(self, k, v):
+		if k[:19] == '_BitFieldInstance__':
+			return object.__setattr__(self, k, v)
+
+		bit = self.__dict[k]
+		self.__value &= ~(1 << bit)
+		self.__value |= bool(v) << bit
+
+	def __str__(self):
+		return '<%s>' % ','.join([ k for k in self.__dict if getattr(self, k) ])
+
+	def __repr__(self):
+		return 'BitFieldInstance(%s, %s, %s)' % (repr(self.__bfname), repr(self.__dict), repr(self.__value))
+
+BitField = BitFieldMetaClass("BitField", (), {})
+__all__ = [ 'BitField' ]
+
+def bftest():
+	class foo(BitField):
+		bar = 3
+		foo = 4
+		bleh = 16
+
+	return foo(16)