string.c: chompped_length chomp_rs

* string.c (chompped_length, chomp_rs): extract from
  rb_str_chomp_bang to share with rb_str_chomp.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48756 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
string.c: local variables

* string.c (rb_str_plus, rb_str_splice_0): extract local
  variables.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48757 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
string.c: term fill

* string.c (rb_str_plus): fill wchar terminator.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48758 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
string.c: term fill

* string.c (rb_str_times): fill wchar terminator.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48759 b2dd03c8-39d4-4d8f-98ff-823fe69b080e