opendir(3) is subject to the same pathological slowdowns on
slow or unreliable filesystems as open(2), so release the GVL
to avoid stalling the entire VM like we do with IO#open
dir.c (nogvl_opendir): new function
(opendir_without_gvl): new function
(dir_initialize): s/opendir/&_without_gvl/
(do_opendir): ditto
dir: release GVL on opendir
opendir(3) is subject to the same pathological slowdowns on
slow or unreliable filesystems as open(2), so release the GVL
to avoid stalling the entire VM like we do with IO#open
(opendir_without_gvl): new function
(dir_initialize): s/opendir/&_without_gvl/
(do_opendir): ditto
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60830 b2dd03c8-39d4-4d8f-98ff-823fe69b080e