IntegerField.to_internal_value coerces decimal to integer; should fail

[bradford281]

The to_internal_value method coerces data to an int, so when a float/decimal is passed, the int value is saved, rather than raising an exception.

[tomchristie]

I'm afraid you'll need to customize the field if you want this behavior.
An integer field that coerces values to an integer wherever possible isn't unreasonable.

While I absolutely understand see why you might want/expect this change, other folks probably wouldn't.

[bradford281]

It just seems inconsistent with Django, as entering floats in a Django form for IntegerField will raise a ValidationError, whereas in DRF 3.x it does not (I believe it did in DRF 2.x).

Strangely enough, the expected ValidationError will be raised if the float is wrapped in a string (the attempt to coerce it to int fails "ValueError: invalid literal...") so it may even be inconsistent with itself. To clarify:
data = 1 # success
data = "1" # success; equivalent to data = 1
data = 0.1 # success; unexpectedly equivalent to data = 0
data = "0.1" # fail; expected ValidationError, in line with Django form validation

This commit seems to return the field to the expected behavior: ryangallen@3e6a149

[ryangallen]

@tomchristie This pull handles cases where values such as 1.0 or "1.0" pass through as integers but values like 1.5 or "1.5" do not. It matches Django's IntegerField validation and I believe is the behavior most developers would expect. Changing a clear decimal value, say 0.4 to 0, is not expected and could have negative consequences in an application.