transcode.c: use string

* transcode.c (econv_opts): get rid of inadvertent ID creation,
  and preserve argument encoding in error messages.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47041 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
ext: prefer RB_TYPE_P over comparison TYPE with constants

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47042 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
ext: get rid of inadvertent ID creation

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47043 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
strscan.c: encoding in messages

* ext/strscan/strscan.c (strscan_aref): preserve argument encoding
  in error messages.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47044 b2dd03c8-39d4-4d8f-98ff-823fe69b080e