git-synchronizer: make it work on MacOSX, too

MacOSX' sed does not understand \t...

We cannot use "case ... $key) ... esac" if inside a "$(...)" clause
because MacOSX' shell gets hopelessly confused by the closing parenthesis
in the case block.

Also, the 1970s called MacOSX that they want their uniq back that does not
even understand the -D option (show all duplicate lines; useful if some
fields are skipped when testing for uniqueness).

As of time of writing, MacOSX has not responded yet.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
git-synchronizer: Special-case SourceForge

SourceForge has enabled the receive.denyNonFastForwards option without a
way to disable it.

Therefore, let's work around that by deleting non-fast-forwarding branches
first, before pushing them again.

This fixes https://github.com/scijava/scijava-scripts/issues/2.

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