wrong location after directive (Mantis 5127)

[damiendoligez]

Transferred from http://caml.inria.fr/mantis/view.php?id=5127
See the Mantis page for the (longish) discussion.

The locations in the Camlp4 ast are completely wrong for the
material that follows a directive. For a two line file

#use "y.ml";;
let a = 5

the location in the StVal node for line 2 has

start_line = 3 (should be 2)
start_bol = 1 (should be 14)
start_off = 1 (should be 14)

the stop location is also wrong.