Using a closed {Cursor,Session,Connection} handle in Python
will not crash the VM on use. ref #485

Uses the event callback for close to give notification on close
of a handle.  For explicit calls to close(), we set the SWIG 'this'
attribute on the containing object to None.

On uses of a handle as an input argument, we check to see if it is
None, or if its 'this' attribute is None, and issue the
appropriate exception.

Includes a set of test cases that parallel Java test cases for the same.
Add automatic throttling for LSM based on merge speed. Update merge_threads.

The automatic throttling starts if there are too many chunks in an LSM tree
that have never been merged.

Increase the default number of LSM merge threads to 2 from 1. Since one
merge thread can now be pretty much dedicated to creating bloom filters.
Merge pull request #800 from wiredtiger/python-auto-close

Using a closed {Cursor,Session,Connection} handle in Python
Skip the huge key/value test until we can detect where it can be run safely (or converted it to C).
Merge branch 'develop' into lsm-merge-throttle
Increase the default value for session_max to 100.  This allocates more space in the connection handle, but otherwise should have minimal impact on performance, because we track the number of sessions in use.

This change was prompted by increasing the default number of LSM merge threads to 2, which means there is an overhead of 3 sessions per LSM tree (2 merge threads and a checkpoint thread).
Improve D3 stats graphs:
- assume a zero Y value if a series is missing a value at a timestamp
- support an optional right Y axis (with "--right" arguments, not yet rendered well)
Merge pull request #819 from wiredtiger/lsm-merge-throttle

Add automatic throttling for LSM based on merge speed. Update merge_threads