MaybeSentinel: resolve or control whitespace

[nschloe]

Whenever there's a MaybeSentinel, a comma/semicolon etc. is inserted if necessary. Usually, instead of only a comma or a semicolon, some whitespace is also inserted, e.g.,

import numpy; import scipy

(Note the space after ;.) I would like to have control over that whitespace. There are at least two possiblities here:

1. Set some property in MaybeSentinel
2. Resolve all MaybeSentinels in a tree and take care of the whitespace after that.

Is there a way to do either of these things?