Save the Typing_deps hashtable as well

Summary: I'm not sure how to create a case that fails without saving the
hashtable, but it seems like something that should be saved...

Reviewed By: @pikatchu

Differential Revision: D1610807
hh_server now accepts a list of files to recheck after load.

Reviewed By: @jwatzman

Differential Revision: D1610916
Don't pass root as an additional parameter.

Summary: It is already available from genv.options, so there's no point
in having it duplicated.

Reviewed By: @elgenie

Differential Revision: D1625185
Fix double-counting of expressions in coverage stats.

Summary: Dedup the count using a Map

Also add --coverage option to hh_single_type_check so we can write unit
tests for coverage results.

Also handle the edge case where there are no expressions at all in a
file.

Reviewed By: @elgenie

Differential Revision: D1625309
Remove unused is_local_array.

Reviewed By: @elgenie

Differential Revision: D1625183