Descriptive error message if field is migrated to be required
Merge branch 'develop' into migration

Conflicts:
	modularodm/storedobject.py
Fix check if field was made required
Fix print statement
Warn user about setting required field

insted of raising error
Merge branch 'develop' into migration

Conflicts:
	modularodm/storedobject.py
	tests/test_migration.py
More correct examples
On branch migration
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

	modified:   modularodm/storedobject.py

Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

	modified:   tests/test_migration.py
Added tests for making field required
Merge pull request #62 from sloria/migration

Warn if field is made required with no default set