xbps-src: fix fetch phase with depends, performance improvements.

- The fetch phase *must* run after installing pkg dependencies,
  otherwise it could fail if we need them for fetching.

- Performance improvements for xbps-src. Only source shutils files
  at the start, not every time we use a function.

xbps-src/shutils/chroot.sh.in

@@ -54,7 +54,6 @@ if [ "${chroot_cmd}" = "chroot" ]; then
 	fi
 fi
 
-. $XBPS_SHUTILSDIR/builddep_funcs.sh
 check_installed_pkg base-chroot-0.11
 if [ $? -ne 0 ]; then
 	echo "${XBPS_MASTERDIR} has not been prepared for chroot operations."