Add a filter for dates

[mikey]

A new class net::stubbles::ipo::request::filter::stubDateFilter should be created that is able to filter timestamps and arbitrary date formats supported by strtotime() into a date object.

[mikey]

Filter class added with r1862.

Next steps: extend filter factory to support the date type, and extend it with a new inPeriod() method to add date related checks.

[mikey]

Support in filter factory added with r1863 and r1864.

Next step: add support for request broker with a date filter annotation.

[mikey]

Date filter annotation added with r1865, r1866 and r1867.