Improves performance of some file operations, fixes some memory leaks, and increases clarity.

* Avoids unnecessary alarm(0) when it is about to be set again, only
cleans up after it’s all done.

* Renames DIRCHAR to LISPDIRCHAR to be more descriptive, adds LISPDIRSTR
for contexts where a string is required rather than a character.

* Avoids leaks of directory structures by ensuring that any opendir()
has a matching closedir(), with a timeout check, on the return path

* Ensures that closedir() calls that could smash errno happen after
errno is saved for Lisp’s consumption

* Simplifies code to take advantage of strlcpy()/strlcat() guarantee
that destination string is NUL terminated

* Reduces number of unnecessary copies into scratch buffer for file name
processing

* Removes some commented out code left over from copy/paste of functions

inc/timeout.h

@@ -38,9 +38,8 @@ extern	unsigned int TIMEOUT_TIME;
   } while (0)
 
 #define	S_TOUT(exp)	\
-  alarm(TIMEOUT_TIME),                  \
-    (exp),                              \
-    alarm(0)
+  alarm(TIMEOUT_TIME),  \
+    (exp)
 
 #define	ERRSETJMP(rval)					\
   do {							\