install-mans: avoid spurious failure with NetBSD make * lib/am/mans.am: After the changes introduced by previous commit v1.11-759-g368f1c4, some manpage installation recipes started to fail spuriously on NetBSD 5.1 make. Apparently, the system make there eats backslashes used to escape whitespace characters in the relevant recipes. Revert to slightly slower but safer idioms that avoid the need of such escaping. Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>