Revert "Ensure installation dirs are built before contents are installed (v2)"

This reverts commit 7f165f2587f6dafe7d4d438136dd959ed5610979.

pending resolution of
http://www.postgresql.org/message-id/1381193255.25702.4.camel@vanquo.pezone.net
Revert "Backpatch pgxs vpath build and installation fixes."

This reverts commit f8110c5f66ad079e3dbc0b66bed06207c43643ef.

pending resolution of
http://www.postgresql.org/message-id/1381193255.25702.4.camel@vanquo.pezone.net
Revert "Document support for VPATH builds of extensions."

This reverts commit 9598134e3030a883ff6eea8a822466ce5143ffeb.