Allow report filtering by month (matching month only, in any year)

This patch adds a new filter operator type, which will allow the user to select one or more months from a list (Jan. to Dec.), and then will return all rows where the date field contains a date within that month in any year.

Example:
Filter: "Date of Birth" for "is one of" "March, April"
Returns: Contacts with birth dates in March or April (including March 1, 1999; March 23, 2001; April 15, 1900; April 7, 1901; etc.)

Note: Deepak and I had discussed adding this operator as OP_MONTH = 5, with the notion that these values are not mean to be checked with bitwise operations. However, there are several places – including some reports and Criteria.tpl – that actually do bitwise checking on these values, so I'm assigning it as OP_MONTH = 128;