Alex notes users might reasonably pass NULL pointers when trying to get
values from statistics cursors, it's a cheap test to make sure we don't
drop core.  Reference #579.
Change a name in the WT_REF.key union.
Update cursor->search_near to handle a NULL exact parameter.
Fix compiler warning.

../src/btree/bt_cursor.c:185: warning: 'exact' may be used uninitialized
in this function
Explicitly clear return references for connection, session and cursor
open, it's just nicer.  Don't clear conn->default_session until there's
a valid replacement, underlying functions use it, it's dangerous to pass
it in as the memory location to store its replacement.
Fix "make install" of Python.  Remove old code and restructure the Python sources under lang/python to simplify the installation step.

--HG--
rename : lang/python/fpacking.py => lang/python/wiredtiger/fpacking.py
rename : lang/python/intpack-test.py => lang/python/wiredtiger/intpack-test.py
rename : lang/python/intpacking.py => lang/python/wiredtiger/intpacking.py
rename : lang/python/packing-test.py => lang/python/wiredtiger/packing-test.py
rename : lang/python/packing.py => lang/python/wiredtiger/packing.py
Merge pull request #598 from wiredtiger/python-install

Fix "make install" of Python.
Pass any configured Python prefix through to the Python install step.
Merge branch 'develop' into logging