Add TFHoliday_AprilFools to TFHoliday enum (bug 6092, r=psychonic).
Update TF2 Ext IsHolidayActive detour to use TF_IsHolidayActive (bug 6094, r=psychonic).
Add new TF2_IsHolidayActive native to TF2 Ext (bug 6095, r=psychonic).