'parallel' proves array bounds

tests/parallel/tforstmt.nim

@@ -0,0 +1,24 @@
+discard """
+  output: '''3
+4
+5
+6
+7'''
+  sortoutput: true
+"""
+
+import threadpool, math
+
+proc p(x: int) =
+  echo x
+
+proc testFor(a, b: int; foo: var openArray[int]) =
+  parallel:
+    for i in max(a, 0) .. min(b, foo.len-1):
+      spawn p(foo[i])
+
+var arr = [0, 1, 2, 3, 4, 5, 6, 7]
+
+testFor(3, 10, arr)
+
+