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/stow_funcs.sh

@@ -23,8 +23,6 @@
 # THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #-
 
-. ${XBPS_SHUTILSDIR}/builddep_funcs.sh
-
 stow_pkg_handler()
 {
 	local action="$1" subpkg spkgrev