[elephant-devel] patches

[Alex Mizrahi]

I've pushed both my patches and fix posted by Nikodemus.

These ones fix general elephant functionality, so code review is welcome:

   * default-pset workaround
   * removed unnecessary MOP manipulations for SBCL (as reported by N. 
Siivola)
   * fix dropping instance with derived index
   * derived index rebuilding, inherited index rebuilding
   * different handling of ensure-schema and compute-derived-index-triggers

These ones are specific to db-postmodern:

   * pset fix
   * pm-pset
   * in place upgrade support