Fix build on Ruby18. We should specify endian for UTF16/32.
define Object#blank? only if not defined yet
Merge pull request #475 from amatsuda/object_blank_redefine_warning

define Object#blank? only if not defined yet
Merge pull request #471 from kennyj/fix_build_on_ruby18

Fix build on Ruby18. We should specify endian for UTF16/32.
Merge remote-tracking branch 'origin/master' into jeremy