Fix parent field name different from 'parent'

[singleton11]

If PolymorphicTreeForeignKey field name has name which different from 'parent' there was an error in admin
Added test for case above
Actualized tox and travis configs
Added step-by-step instruction to readme how to run tests
Adjusted supported version list in readme

[codecov-io]

Current coverage is 54.87% (diff: 98.76%)

Merging #57 into master will increase coverage by 9.55%

@@ master #57 diff @@ ========================================== Files 12 13 +1 Lines 631 707 +76 Methods 0 0 Messages 0 0 Branches 0 0 ========================================== + Hits 286 388 +102  + Misses 345 319 -26  Partials 0 0 

Powered by Codecov. Last update 61debd4...06e26a0

[singleton11]

Added possibility to make validation before move node in admin through can_be_moved method of PolymorphicMPTTModel overriding. This method calls in admin, and if there are exceptions during execution, error response returns

[vdboor]

Thanks for this wonderful work!

[vdboor]

@singleton11 I do wonder, is can_be_moved() needed? For example, there is already can_have_children() which does about the same thing. Where are you using that hook for?

I've also merged some other fixes, so please merge/rebase before you add a new fix ;-)

[vdboor]

@singleton11 FYI, I've renamedcan_move_to() to validate_move_to()
Since we can limit the children types now, would you still need validate_move_to() to exist?
Thanks for letting me know!

[singleton11]

@vdboor, I promise, I will send different features as separate PRs next time ;-)

mptt doesn't call clean() to check, if validation error occurs, when move_to() executed.

Yes, I need to do clean() before moving. Hovewer it's not a django-polymorhic-tree problem, therefore I made this hook. I don't know where to add clean() calling in django-mptt