Convert to boolean in C code

casecmp?(str) is 1.5x faster than casecmp(str).zero?
It's 1 less method call in Ruby, and the C code can convert
to boolean, rather than returning a number and determining
if it's zero.

config/initializers/open_uri_redirection.rb

@@ -2,7 +2,7 @@ require 'open-uri'
 
 module OpenURI
   def self.redirectable?(uri1, uri2) # :nodoc:
-    uri1.scheme.casecmp(uri2.scheme).zero? ||
+    uri1.scheme.casecmp?(uri2.scheme) ||
       (/\A(?:http|https|ftp)\z/i =~ uri1.scheme && /\A(?:http|https|ftp)\z/i =~ uri2.scheme)
   end
 end