compat: Add a 'usleep' shim for Mes.

* gash/compat.scm [mes] (usleep): New procedure.

gash/compat.scm

@@ -108,6 +108,7 @@
           thunk?
           EXIT_SUCCESS
           EXIT_FAILURE
+          usleep
           exact?
           exact-integer?
           set-program-arguments
@@ -253,6 +254,13 @@
   (define EXIT_SUCCESS 0)
   (define EXIT_FAILURE 1)
 
+  ;; Mes doesn't have sleep, so we just spin the tires a bit.
+  (define (usleep n)
+    (let loop ((n n))
+      (if (<= n 0)
+          #t
+          (loop (- n 1)))))
+
   ;; Mes only has exact integers.
   (define exact? integer?)
   (define exact-integer? integer?)