Better support for dot-format (e.g. 13.1.2009) with ambiguousMMDD

[skius]

While the dot format is currently supported for MM.DD.YYYY, this format does not set the ambiguousMMDD flag. This leads to issues mainly in fixes for #28 (such as #89), where ambiguousMMDD needs to be set.

The way I see it, ambiguousMMDD needs to be set for all ambiguous date formats (regardless the separator).

(FWIW, I'm pretty sure the dot separator is mostly used in DD.MM.YY[YY] formats anyway.)