add -p: import Term::ReadKey with 'require'

eval{use...} is no good because the 'use' is evaluated at compile
time, so manually 'require' it.  We need to forward declare the
functions we use, otherwise Perl raises a compilation error.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-add--interactive.perl

@@ -40,9 +40,12 @@
 my $normal_color = $repo->get_color("", "reset");
 
 my $use_readkey = 0;
+sub ReadMode;
+sub ReadKey;
 if ($repo->config_bool("interactive.singlekey")) {
 	eval {
-		use Term::ReadKey;
+		require Term::ReadKey;
+		Term::ReadKey->import;
 		$use_readkey = 1;
 	};
 }