Allow 65 knots threshold for landing stop, especially where Airspeed is not recorded below 60 knots and therefore Airspeed True has a little more than that. Should values not be calculated due to masks, use the original landing slice values to protect the landing roll from creating slices outside of the roll!
ground track precise fix - where no speed raise valueerror rather than returning masked array which may have issues.
fix for NotImplementedError.
create_kpvs_where_state replaced with create_kpvs_where which accepts a conditional argument (resulting in a boolean array).
Added test cases for phase argument which weren't present before. In addition, now accepts a slice, list of slices, Section or list of Sections.
hdf.dependency_tree replaced graph_adjacencies with json_grah.dumps which is available in networkx v1.7 - means that entire graph can be loaded rather than the adjacencies representation.
Circular Dependency now handled by dependency graph - by creating a branch path we can check if the node has been previously requested and therefore it cannot yet be available (circular depenency of node dependencies!).

Legitimate examples are:
* Heading <-> Heading True (via Magnetic Variation)
* Gear Down Selected <-> Gear Down

Updated docstrings with better explanations.
Gear Down can now depend upon Gear Down Selected due to previous circular dependency fix in dependency graph
comment added about slow calculation
AP Disengaged using create_kpvs_where
comment about good use of cache
Merge branch 'master' of github.com:FlightDataServices/FlightDataAnalyzer
key point values create_kpvs_where_state(...) replaced with new create_kpvs_where(condition...)