Define and use a path separator string

A colon can't be used to separate paths on Windows since they are used
in drive sepecification.  Define a macro that can be used as a path
separator string.  On Windows, this is defined as ";".  It is a ":"
everywhere else.

include/config.h.w32

@@ -99,9 +99,12 @@ static const char *const rcsid[] = { (const char *)rcsid, "@(#)" msg }
 
 @FEATURE_DEFS@
 
-/* Define is backslashes act as path delimiters */
+/* Define is backslashes act as path name delimiters */
 #define BACKSLASH_PATH_DELIM 1
 
+/* Path separator character */
+#define PATH_SEP ";"
+
 /* Define if you want to use DES encryption in telnet. */
 #define DES_ENCRYPTION 1