Russian months recognition fixed

The problem is in contructing RegExp for matching against input date. In russian language words sometimes changes their ending, causing some troubles.

The bug was in dates like this: `11 мая 1989` with format `D MMMM YYYY` (which is May, 11)

moment.js parser says it is January, 11.

Also, monthsCaseReplace function definitions looks a little bit strange accepting second attribute `format`, because there is an empty string passing in moment.js code:

    #line 406
    regex = '^' + this.months(mom, '') + '|^' + this.monthsShort(mom, '');