Fixes resolving to db_field from class field name, in distinct() query.
Merge conflicts resolved.
Removed merge trackers in code, merged correctly now.
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Corrected spelling mistakes, some grammar, and UUID/DecimalField error in upgrade.rst
Merge pull request #409 from bool-dev/master

Corrected mistakes in upgrade.rst documentation