Convert initial value that comes as int to a list of flag names.

[zaxl]

When editing an object the widget works as expected.
Exception occurs when adding a new object.

[dcramer]

needs a space after the comma

also initial isnt guaranteed to be in kwargs

[dcramer]

My feedback is all stylistic though I think the approach may not be very correct. This is making the assumption that there's a 64 bit integer.

[zaxl]

Thanks for the feedback!.
I'm not a python expert but

isl = 1 << 63
type (isl) == int
False
type (isl) == long
True

The shift operation is promoted to long when int is 32 bits.
BigIntegerField which is the base field is also guaranteed to be 64 bits.

[SeanHayes]

This can be cancelled once #63 is merged.

Refs #58