smart match overloading

Conflicts:
	Changes
work with pre-5.10.0

Only test working with switch if switch exists.

It's safe to leave the actual definition of ~~ overloading in the module,
because in earlier versions of Perl it just gets ignored.
plan skip_all does exit
turn off experimental ~~ warnings
v1.703

        - overload tolerances for ~~ operator (thanks, Smylers!)