Add a test for the ancestors flag to tree_info
Add a test for print_debug_info
Deuglify the print_debug_info unittest by adding a `file` argument

The argument name is inspired by Python3's print function.
Add tests for full tree and drilldown template tags
report real failures
Merge branch 'fix-tests' of git://github.com/ticosax/django-mptt

* 'fix-tests' of git://github.com/ticosax/django-mptt:
  report real failures
cast primary-key value with field before sending to database.

Needed when UUID column type is used as primary key
Test UUID support
Fix travis installation
remove obsolete requirements.txt