Remove comment on errno=0 lines, but add mention to port/strtol.c function.

src/port/strtol.c

@@ -44,6 +44,15 @@ static char sccsid[] = "@(#)strtol.c	5.4 (Berkeley) 2/23/91";
 
 #define const
 
+/*
+ *	Usage Tip:
+ *
+ *	strtol() doesn't give a unique return value to indicate that errno
+ *	should be consulted, so in most cases it is best to set errno = 0
+ *	before calling this function, and then errno != 0 can be tested
+ *	after the function completes.
+ */
+ 
 /*
  * Convert a string to a long integer.
  *