Makes gcc to generate a pshufd instruction for pset1
Revert previous change and introduce a new workaround regarding gcc generating a shufps instruction instead of the more efficient pshufd instruction.
The trick consists in introducing a new pload1 function to be used in low level product kernels for which bug 203 does not apply.
Indeed, it turned out that using inline assembly prevents gcc of doing a good job at instructtion reordering.