Change the user used by fdm if run as root to 'debianfdm' instead of '_fdm'
which is not allowed in debian. (Actually I don't quite remember if it's
strictly not permitted by debian's policy, but I've stopped caring.)

Index: fdm-1.6/MANUAL
===================================================================
--- fdm-1.6.orig/MANUAL.in	2009-04-14 06:00:40.000000000 +0200
+++ fdm-1.6/MANUAL.in	2009-04-14 06:01:02.000000000 +0200
@@ -91,11 +91,11 @@
 	$ export PREFIX=/opt		# defaults to /usr/local
 	$ sudo make install
 
-If being run as root, fdm requires a user named "_fdm" to exist. It will drop
+If being run as root, fdm requires a user named "debianfdm" to exist. It will drop
 privileges to this user and its primary group. The user may be added on
 OpenBSD with, for example:
 
-	# useradd -u 999 -s /bin/nologin -d /var/empty -g=uid _fdm
+	# useradd -u 999 -s /bin/nologin -d /var/empty -g=uid debianfdm
 
 It is not necessary to add a user if fdm is always started by a non-root user.
 
Index: fdm-1.6/fdm.h
===================================================================
--- fdm-1.6.orig/fdm.h	2009-04-14 06:00:40.000000000 +0200
+++ fdm-1.6/fdm.h	2009-04-14 06:01:02.000000000 +0200
@@ -49,7 +49,7 @@
 #include <openssl/ssl.h>
 #include <openssl/err.h>
 
-#define CHILDUSER	"_fdm"
+#define CHILDUSER	"debianfdm"
 #define CONFFILE	".fdm.conf"
 #define SYSCONFFILE	"/etc/fdm.conf"
 #define LOCKFILE	".fdm.lock"