ignore error codes when cleaning
merge Ruby r41855

Revert r41786 "broken utf-8"

revert unexpected commit
merge Ruby r46309

constify rb_encoding and OnigEncoding

* include/ruby/encoding.h: constify `rb_encoding` arguments.
* include/ruby/oniguruma.h: constify `OnigEncoding` arguments.
Merge branch 'master' into tmp/ruby-2.0.x