Ignore clearly incorrect entries when guessing day of month padding when adding changelog entry

[nforro]

For example, scipy has:

* Mon Dec  11 2006 Jef Spaleta <jspaleta@gmail.com> - 0.5.1-5
- Bump for rebuild against python 2.5 in devel tree

An entry like this should be ignored, otherwise there will always be at least 2 spaces of padding.

[lbarcziova]

Still relevant, but should be really low prio (some older specfiles).