[PATCH] Fix to installing non-xs ext's in priv lib

Previous work to flatten the dirs under ext/ resulted in installperl
installing non-XS extensions under archlib.  The attached patch fixes
this.

• [PATCH] Fix to installing non-xs ext's in priv lib by Jerry D. Hedden
• Re: [PATCH] Fix to installing non-xs ext's in priv lib by Rafael Garcia-Suarez