This patch to coq-8.3pl2 fixes a bug in "exists_dir", and will leave many fewer file descriptors unclosed.

     Dan Grayson

diff -ur ../coq-8.3pl2-clean/lib/system.ml ./lib/system.ml
--- ../coq-8.3pl2-clean/lib/system.ml	2010-12-24 03:55:54.000000000 -0600
+++ ./lib/system.ml	2011-10-14 12:49:30.000000000 -0500
@@ -103,7 +103,7 @@
 (* All subdirectories, recursively *)
 
 let exists_dir dir =
-  try let _ = opendir dir in true with Unix_error _ -> false
+  try let _ = closedir (opendir dir) in true with Unix_error _ -> false
 
 let skipped_dirnames = ref ["CVS"; "_darcs"]