* win32/win32.c, include/ruby/win32.h (rb_w32_utruncate): implements new
	  truncate alternative which accepts UTF-8 path.

	* file.c (truncate): use above function.
	  [Bug #12340]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_2@55347 b2dd03c8-39d4-4d8f-98ff-823fe69b080e