Ignore executing install/remove scripts if XBPS_TARGET_ARCH is set.

Instead a two stage approach is necessary when packages for target arch
are installed:

	- XBPS_TARGET_ARCH=arch xbps-install foo <- only unpack
	- xbps-reconfigure -a <- configure natively or via an emulator

include/xbps_api.h.in

@@ -48,7 +48,7 @@
  */
 #define XBPS_PKGINDEX_VERSION	"1.7"
 
-#define XBPS_API_VERSION	"20130307-1"
+#define XBPS_API_VERSION	"20130307-2"
 
 #ifndef XBPS_VERSION
  #define XBPS_VERSION		"UNSET"
@@ -544,7 +544,8 @@ struct xbps_handle {
 	 */
 	char *cachedir_priv;
 	char *metadir_priv;
-	char *un_machine;
+	char *native_arch;
+	const char *target_arch;
 	/*
 	 * @var repository
 	 *