[IMP] Call 'only_create' mapping functions only when the mapper is called  with for_create=True
Merge pull request #25 from acsone/7.0-improve-only_create-mapping

[IMP] Call 'only_create' mapping functions only when the mapper is ...

...called with for_create=True

Some mapping functions can be resource intensive. The change avoids
calling functions annotated with 'only_create' if the mapper is not
called with for_create=True and thus reduces resource consumption in
such cases.

Conflicts:
	connector/unit/mapper.py