Fix: pipchecker, pip 10.0.0 compatibility
Fix: sqldiff, improve support of GIS fields by using Django introspection
Fix: shell_plus, fix bug in windows when PYTHONPATH is defined
Fix: shell_plus, Call execute on CursorWrapper instead of directly on cursor to ensure wrappers are run
Fix: runserver_plus, Call execute on CursorWrapper instead of directly on cursor to ensure wrappers are run
Improvement: sqldiff, drop old compatibility code
Improvement: ForeignKeyAutocompleteAdminMixin, improvements for Django >1.9