Enhancement - Sequence range limiting

- Prevents overly large ranges.  A bug was reported from a user
  who tried this:

    % task annotate 1 1-987654321

  The 1-987654321 was assumed to be a valid range, and caused task
  to consume all available memory.  The workaround was:

    % task 1 annotate 1-987654321

  But it seems a good idea to range-limit sequences.  Currently
  it is 1000.  Perhaps this should be configurable.

src/tests/seq.t.cpp

@@ -90,7 +90,7 @@ int main (int argc, char** argv)
   seq = parseSequence ("1--2");
   t.is (seq.size (), (size_t)0, "seq '1--2' -> 0 items (error)");
 
-  // 1-1000
+  // 1-1000 (SEQUENCE_MAX);
   seq = parseSequence ("1-1000");
   t.is (seq.size (), (size_t)1000, "seq '1-1000' -> 1000 items");
   if (seq.size () == 1000)