Follow behaviour of IO#ungetbyte

	see r65802 and [Bug #14359]

	* expand tabs.

	setbyte / ungetbyte allow out-of-range integers

	* string.c: String#setbyte to accept arbitrary integers [Bug #15460]

	* io.c: ditto for IO#ungetbyte

	* ext/strringio/stringio.c: ditto for StringIO#ungetbyte



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_6@66845 b2dd03c8-39d4-4d8f-98ff-823fe69b080e