ADD: Allow pending requests to be canceled via "Backend.Request.cancel[All]()".
FIX: Update inappropriate copyright notice.
ADD: "Backend.Sqlite.query()": Show call stack trace if query is null.
Merge branch 'master' into python2.7

- ADD: "Backend.Sqlite.query()": Show call stack trace if query is null.
- FIX: Update inappropriate copyright notice.
- ADD: Allow pending requests to be canceled via "Backend.Request.cancel[All]()".