coccinelle: remove parentheses that become unnecessary

coccinelle: remove parentheses that become unnecessary

Transformations that hide multiplications can end up with an pair of
parentheses that is no longer needed.  E.g. with a rule like this:

  @@
  expression E;
  @@
  - E * 2
  + double(E)

... we might get a patch like this:

  -	x = (a + b) * 2;
  +	x = double((a + b));

Add a pair of parentheses to the preimage side of such rules.
Coccinelle will generate patches that remove them if they are present,
and it will still match expressions that lack them.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>