'parallel' statement: next steps

tests/parallel/tnon_disjoint_slice1.nim

@@ -0,0 +1,25 @@
+discard """
+  errormsg: "cannot prove (i)..(i) disjoint from (i + 1)..(i + 1)"
+  line: 20
+"""
+
+import threadpool
+
+proc f(a: openArray[int]) =
+  for x in a: echo x
+
+proc f(a: int) = echo a
+
+proc main() =
+  var a: array[0..30, int]
+  parallel:
+    #spawn f(a[0..15])
+    #spawn f(a[16..30])
+    var i = 0
+    while i <= 29:
+      spawn f(a[i])
+      spawn f(a[i+1])
+      inc i
+      #inc i  # inc i, 2  would be correct here
+
+main()