add an explicit 'int' to the main declaration in 300.c; also add an exit(0) for whiny C compilers; lowercase the title in limits.t

tests/limits.t

@@ -1,6 +1,6 @@
 . tests/functions.sh
 
-title 'Recursion limits'
+title 'recursion limits'
 rc=0
 
 limits() {

tools/300.c

@@ -1,6 +1,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 
+int
 main(argc, argv)
 int argc;
 char **argv;
@@ -33,4 +34,5 @@ char **argv;
 	    printf("%s", pattern2);
 
     putchar('\n');
+    exit(0);
 }