Calendar width is broken in IE

In IE6 and IE7, the width of the calendar div is unset, so it defaults to the width of the viewport. This patch sets the width to 16em, which fixes IE and doesn't change the display in FF or Safari.

This patch also sets the default margin of the calendar table to 0; our theme sets margins for all table elements, which causes extra margins to be shown around the calendar.

Enjoy!