* string.c (coderange_scan): extracted from rb_enc_str_coderange.
(rb_enc_str_coderange): use coderange_scan.
(rb_str_shared_replace): copy encoding and coderange.
(rb_enc_str_buf_cat): new function for linear complexity string
accumulation with encoding.
(rb_str_sub_bang): don't conflict substituted part and replacement.
(str_gsub): use rb_enc_str_buf_cat.
(rb_str_clear): clear coderange.
* re.c (rb_reg_regsub): use rb_enc_str_buf_cat.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@14910 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
