Added requirement for developer system to have gnu libtool

git-svn-id: https://nagiosplug.svn.sourceforge.net/svnroot/nagiosplug/nagiosplug/trunk@1326 f882894a-f735-0410-b71e-b25c423dba1c

doc/developer-guidelines.sgml

@@ -58,6 +58,7 @@
 	automake 1.8
 	autoconf 2.58
 	gettext 0.11.5
+	gnu libtool 1.5.6
 	</literallayout>
 
 	To compile from CVS, after you have checked out the code, run: