Added initial support to install binpkgs to resolve builddeps.

if XBPS_PREFER_BINPKG_DEPS is set in xbps-src.conf, the local binpkg
repo in XBPS_PACKAGESDIR will be used to install binpkgs.

To use this feature you'll need xbps utils >= 20100114 from head.

--HG--
extra : convert_revision : 7317e0e2741997007e81ed478f819c36e4858e5d

xbps-src/shutils/builddep_funcs.sh

@@ -119,6 +119,10 @@ install_dependencies_pkg()
 	[ -z "$notinstalled_deps" ] && return 0
 
 	for i in ${notinstalled_deps}; do
+		if [ -n "$XBPS_PREFER_BINPKG_DEPS" ]; then
+			install_pkg_with_binpkg ${i}
+			[ $? -ne 0 ] && exit $?
+		fi
 		pkgn=$($XBPS_PKGDB_CMD getpkgdepname ${i})
 		check_pkgdep_matched "${i}"
 		[ $? -eq 0 ] && continue