SF #665913, Fix mmap module core dump with unix

Closing an mmap'ed file (calling munmap) twice on Solaris caused a core dump.
diff --git a/Misc/NEWS b/Misc/NEWS
index d2d4f8a..b9d108a 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -69,6 +69,9 @@
   possible to have timestamps that differ by a second, yet where
   datetimes constructed from them are equal.
 
+- Fix a crash on Solaris that occurred when calling close() on
+  an mmap'ed file which was already closed.  (SF patch #665913)
+
 Library
 -------