Allow `add -p` and `add -i` with a large number of files

This fixes https://github.com/msysgit/git/issues/182.

Inspired by Pull Request 218 using code from @PhilipDavis.

[jes: simplified code quite a bit]

Signed-off-by: Kelly Heller <kkheller@cedrus.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

git-add--interactive.perl

@@ -160,6 +160,24 @@ sub run_cmd_pipe {
 		die "$^O does not support: @invalid\n" if @invalid;
 		my @args = map { m/ /o ? "\"$_\"": $_ } @_;
 		return qx{@args};
+	} elsif (($^O eq 'MSWin32' || $^O eq 'msys') && (scalar @_ > 200) &&
+			grep $_ eq '--', @_) {
+		use File::Temp qw(tempfile);
+		my ($fhargs, $filename) =
+			tempfile('git-args-XXXXXX', UNLINK => 1);
+
+		my $cmd = 'cat '.$filename.' | xargs -0 -s 20000 ';
+		while ($_[0] ne '--') {
+			$cmd = $cmd . shift(@_) . ' ';
+		}
+
+		shift(@_);
+		print $fhargs join("\0", @_);
+		close($fhargs);
+
+		my $fh = undef;
+		open($fh, '-|', $cmd) or die;
+		return <$fh>;
 	} else {
 		my $fh = undef;
 		open($fh, '-|', @_) or die;