Recent patches:
* set-valued slot tests, optimized postmodern support
* test-slot-sets enabled in asd
test-slot-sets thoroughly verifies current behaviour (rather weird)
optimized postmodern support uses pm-pset for backend storage which
keeps everything in one btree (database table)
*
I've fixed problem with db-postmodern, now it passes almost all tests on
SBCL 1.0.16 (except NIL-SLOT-CLASS).
The problem was that with-btree-cursor using WITHOUT-INTERRUPTS while
making cursor to prevent potential resource leak, but POSTMODERN depends
on interrupts for socket communications (
