jack: enhanced to build if libcap is not available

audio/jack/jack.conf

@@ -2,6 +2,7 @@
 # This copyright note is auto-generated by ./scripts/Create-CopyPatch.
 #
 # Filename: package/.../jack/jack.conf
+# Copyright (C) 2009 The OpenSDE Project
 # Copyright (C) 2004 - 2006 The T2 SDE Project
 #
 # More information can be found in the files COPYING and README.
@@ -12,5 +13,7 @@
 # GNU General Public License can be found in the file COPYING.
 # --- SDE-COPYRIGHT-NOTE-END ---
 
-var_append confopt " " "--enable-capabilities"
+if pkginstalled libcap; then
+	var_append confopt " " "--enable-capabilities"
+fi