Update requirements.txt

`httplib2` 0.5.0 is not available anymore from pypi.
Fix broken http test for bad encoding.
Update requirements.txt etc

There were a couple of pins to very old package versions, plus
extra modules are needed for running the test suite.
Fixed failing get_bad_encoding test.
Support forwards-reference in Link

Added failing test for Link forwards-reference support.  Extended
string forwards-reference support to Link as well as Object.
Don't try to update from a response that has no content.
Handle null for collection properties in response

Currently if None/null is found where a List or Dict is expected,
decoding throws:

  TypeError: 'NoneType' object is not iterable

This change solves the problem by safely making the value 'None'
in the built object.

[this version has been modified from Christian's original version; it
 inserts a 'None' property into the returned value rather than an
 empty list]
More liberal parsing of datetime timestamps

Currently, datetime values which were not formatted in exactly the
right format would raise a TypeError when parsed.  To handle them
better, add the dateutil dependency, which is capable of parsing a
wide range of valid ISO8601 datetime strings (and some invalid strings
as well).
Sync with github mater

Conflicts:
	requirements.txt
Release engineering for 1.2.2 (proposed)
Merge branch 'master' of https://github.com/saymedia/remoteobjects