Ruby

Signal.list deduplicates keys

This allows us to reuse string objects used in symbols as well
as any string representations of signal names in source code.

• signal.c (sig_list): use fstring for hash key
• test/ruby/test_signal.rb (test_signal_list_dedupe_keys): added

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53657 b2dd03c8-39d4-4d8f-98ff-823fe69b080e