Correct help blurb in checkout -p and friends

When git checkout -p from the index or HEAD is run in edit mode, the
help message about removing '-' and '+' lines was backwards. Because it
is reverse applying the patch, the meanings of '-' and '+' are reversed.

Signed-off-by: Jonathan "Duke" Leto <jonathan@leto.net>
Acked-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-add--interactive.perl

@@ -87,6 +87,7 @@ my %patch_modes = (
 		TARGET => '',
 		PARTICIPLE => 'staging',
 		FILTER => 'file-only',
+		IS_REVERSE => 0,
 	},
 	'stash' => {
 		DIFF => 'diff-index -p HEAD',
@@ -96,6 +97,7 @@ my %patch_modes = (
 		TARGET => '',
 		PARTICIPLE => 'stashing',
 		FILTER => undef,
+		IS_REVERSE => 0,
 	},
 	'reset_head' => {
 		DIFF => 'diff-index -p --cached',
@@ -105,6 +107,7 @@ my %patch_modes = (
 		TARGET => '',
 		PARTICIPLE => 'unstaging',
 		FILTER => 'index-only',
+		IS_REVERSE => 1,
 	},
 	'reset_nothead' => {
 		DIFF => 'diff-index -R -p --cached',
@@ -114,6 +117,7 @@ my %patch_modes = (
 		TARGET => ' to index',
 		PARTICIPLE => 'applying',
 		FILTER => 'index-only',
+		IS_REVERSE => 0,
 	},
 	'checkout_index' => {
 		DIFF => 'diff-files -p',
@@ -123,6 +127,7 @@ my %patch_modes = (
 		TARGET => ' from worktree',
 		PARTICIPLE => 'discarding',
 		FILTER => 'file-only',
+		IS_REVERSE => 1,
 	},
 	'checkout_head' => {
 		DIFF => 'diff-index -p',
@@ -132,6 +137,7 @@ my %patch_modes = (
 		TARGET => ' from index and worktree',
 		PARTICIPLE => 'discarding',
 		FILTER => undef,
+		IS_REVERSE => 1,
 	},
 	'checkout_nothead' => {
 		DIFF => 'diff-index -R -p',
@@ -141,6 +147,7 @@ my %patch_modes = (
 		TARGET => ' to index and worktree',
 		PARTICIPLE => 'applying',
 		FILTER => undef,
+		IS_REVERSE => 0,
 	},
 );
 
@@ -999,10 +1006,12 @@ sub edit_hunk_manually {
 	print $fh "# Manual hunk edit mode -- see bottom for a quick guide\n";
 	print $fh @$oldtext;
 	my $participle = $patch_mode_flavour{PARTICIPLE};
+	my $is_reverse = $patch_mode_flavour{IS_REVERSE};
+	my ($remove_plus, $remove_minus) = $is_reverse ? ('-', '+') : ('+', '-');
 	print $fh <<EOF;
 # ---
-# To remove '-' lines, make them ' ' lines (context).
-# To remove '+' lines, delete them.
+# To remove '$remove_minus' lines, make them ' ' lines (context).
+# To remove '$remove_plus' lines, delete them.
 # Lines starting with # will be removed.
 #
 # If the patch applies cleanly, the edited hunk will immediately be