make htop trunk compile on FreeBSD 8.2-STABLE

(thanks to Trond Endestrol)

ChangeLog

@@ -5,6 +5,8 @@ What's new in version 1.0.1
   respecting $XDG_CONFIG_HOME 
   (thanks to Hadzhimurad Ustarkhan for the suggestion.)
 * Safer behavior on the kill screen, to make it harder to kill the wrong process.
+* Fix for building in FreeBSD 8.2
+  (thanks to Trond Endrestol)
 * BUGFIX: keep main panel up-to-date when running the screen manager,
   to fix crash when processes die while on the F9/Kill screen.
 

TraceScreen.c

@@ -20,6 +20,7 @@ in the source distribution for its full text.
 #include <fcntl.h>
 #include <sys/types.h>
 #include <sys/wait.h>
+#include <signal.h>
 
 /*{
 #include "Process.h"