[core] Change library loading so an extension is required. Alternate extension checks are performed, but only PIR->PBC, PASM->PBC and PBC->PIR/PASM. This means that loading a library will perform at most 3 extension checks, with the common case being 1 or 2.
[core] Change library loading so an extension is required. Alternate extension
checks are performed, but only PIR->PBC, PASM->PBC and PBC->PIR/PASM. This
means that loading a library will perform at most 3 extension checks, with the
common case being 1 or 2.


git-svn-id: 6e74a02f85675cec270f5d931b0f6998666294a3@35928 d31e2699-5ff4-0310-a27c-f18f2fbe73fe

FROGGS/parrot,tkob/parrot,FROGGS/parrot,youprofit/parrot,tkob/parrot,FROGGS/parrot,youprofit/parrot,gitster/parrot,tkob/parrot,gitster/parrot,fernandobrito/parrot,youprofit/parrot,youprofit/parrot,parrot/parrot,tkob/parrot,youprofit/parrot,gagern/parrot,fernandobrito/parrot,gitster/parrot,fernandobrito/parrot,tewk/parrot-select,FROGGS/parrot,parrot/parrot,youprofit/parrot,tewk/parrot-select,tkob/parrot,tkob/parrot,gitster/parrot,fernandobrito/parrot,FROGGS/parrot,FROGGS/parrot,FROGGS/parrot,gagern/parrot,tkob/parrot,gagern/parrot,gitster/parrot,tewk/parrot-select,tewk/parrot-select,parrot/parrot,fernandobrito/parrot,FROGGS/parrot,gagern/parrot,parrot/parrot,gagern/parrot,youprofit/parrot,fernandobrito/parrot,fernandobrito/parrot,tkob/parrot,tewk/parrot-select,youprofit/parrot,tewk/parrot-select,gitster/parrot,gagern/parrot,parrot/parrot,tewk/parrot-select,gagern/parrot,gitster/parrot