[perl #120232] [BUG] sprintf doesn't format %floats with many significant digits properly

[Christian Bartolomaeus via RT]

This works for Moar, Parrot and JVM:

$ perl6 -e 'printf("%.50f", 1.115)'
1.11500000000000000000000000000000000000000000000000

I added a test to S32-str/sprintf.t with the following commit: 
https://github.com/perl6/roast/commit/46ef5bf0e9. I'm closing the ticket.