Ticket #10447 - SQL Optimization for Program Listing

This adds a 24 hour cap on the starttime of program listings returned from mythfrontend/guidegrid.cpp and mythbackend/guide.cpp, which gives a performance boost of anywhere from 2x to 3x depending on the where clause of some of the queries. By putting this cap, large number of disk seeks and table lookups are avoided to filter out programs with invalid end times for the query