abuild.in: ensure that $triggers is not in $source

Since we already check that $install is not in $source is does make
sense to also check that $triggers is not in $source.

abuild.in

@@ -180,6 +180,11 @@ default_sanitycheck() {
 			die "$p: trigger script does not match pkgname or any subpackage"
 		fi
 
+		if source_has "$f"; then
+			warning "You should not have \$triggers in source"
+			continue
+		fi
+
 		[ -e "$startdir"/$f ] || die "trigger script $f is missing"
 	done
 	if [ -n "$source" ]; then