[PATCH] filter-branch: use $(($i+1)) instead of $((i+1))

The expression $((i+1)) is not portable at all: even some bash versions do not grok it. So do not use it.

Noticed by Jonas Fonseca.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---

	On Tue, 5 Jun 2007, Jonas Fonseca wrote:
	
	> Junio C Hamano <gitster@pobox.com> wrote Tue, Jun 05, 2007:
	> > Jonas Fonseca <fonseca@diku.dk> writes:
	> > 
	> > > $ git filter-branch H2
	> > > /home/fonseca/bin/git-filter-branch: 386: arith: syntax error: "i+1"
	> > > $
	> > >
	> > > A possible fix that makes the test pass for me.
	> >
	> > [...]
	> >
	> > The portable ones we already have in the code say things like:
	> > 
	> > 	msgnum=$(($msgnum+1))
	> 
	> Yes, I should have investigated before sending.
	> 
	> > The one in filter-branch that bit you does not dereference 'i'.
	> > I am reasonably sure if you fix it to read:
	> > 
	> > 	i=$(( $i+1 ))
	> > 
	> > dash would grok it.
	> 
	> This works here. Even without the spaces.

	Voila.

 git-filter-branch.sh |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)