git-gui: introduce function git_redir for git calls with redirections

git-gui: introduce function git_redir for git calls with redirections

Proc git invokes git and collects all output, which is it returns.
We are going to treat command arguments and redirections differently to
avoid passing arguments that look like redirections to the command
accidentally. A few invocations also pass redirection operators as
command arguments deliberately. Rewrite these cases to use a new
function git_redir that takes two lists, one for the regular command
arguments and one for the redirection operations.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Taylor Blau <me@ttaylorr.com>