Fix a dumb mistake in an error message, where I put '%' in the format

string instead of '%i.

Also, build libnetmon with debugging symbols so that if we are able to
make it dump core, we can hopefully find out useful information.

pelab/libnetmon/GNUmakefile

@@ -7,7 +7,7 @@
 SYSTEM :=	$(shell uname -s)
 
 # I like using -pedantic, but it gives us some trouble with function pointers
-CFLAGS=-Wall -Werror -std=c99
+CFLAGS=-Wall -Werror -std=c99 -g
 
 ifeq ($(SYSTEM),Linux)
     LD_FLAGS=-ldl

pelab/libnetmon/libnetmon.c

@@ -708,7 +708,7 @@ void printlog(logmsg_t type, int fd, ...) {
             if (!monitor_udp) { print = false; }
             print_value = false;
         default:
-            croak("Invalid type (%) passed to printlog()\n",type);
+            croak("Invalid type (%i) passed to printlog()\n",type);
     }
 
     /*