Miscellaneous cleanup

Small miscellaneous changes:
Don't exit quietly if no programs are found.
Don't use $countdown if only one program is available, else $countdown > 0 would make $binindex negative.
Don't call clear when only one program is available/dialog is not called.
Check if directories exist before try to `find` files in them, so `find` doesn't print the error to console.
Add '/usr/share/xsessions' to comments of cdmrc as possible sessions location.