Module Diff and Equilibrated pretty print

Mon Oct 1 21:47:55 CEST 2007

Added module Diff in Camlp5 library to compare two arrays (using
the algorithm of the Unix 'diff' command). Added flag 'E' in
pretty print kit in revised syntax (pr_o.cmo) to allow display
equilibrate cases (all cases in 'match' statement are cut if one
is cut, and same equilibration in 'if' statement).