disjoint checker is somewhat smarter

tests/parallel/tdont_be_stupid.nim

@@ -0,0 +1,15 @@
+
+import threadpool, os
+
+proc single(time: int) =
+  sleep time
+  echo time
+
+proc sleepsort(nums: openArray[int]) =
+  parallel:
+    var i = 0
+    while i <= len(nums) + -1:
+      spawn single(nums[i])
+      i += 1
+
+sleepsort([50,3,40,25])