I found a nicer solution to my problem of making review-board work with Git. Indeed I've read the manual! so intead of my svn-diff.pl: you can also install the command-line post-review tool that also does tons of other useful things. With that tool do:
post-review --parent trunk -n
to generate a diff that you can upload in review board.
I'm searching for the right way of actually submitting this patch directly to a svn review-board repository (review board can apparently be hooked into a git repo directly too), but so far I haven't read in the manual that it was possible.
