Make the declaration of the non-standard built-in predicate block/3 in SWI-Prolog conditional on its availability (this predicate was removed in SWI-Prolog 5.9.9).
Make the declaration of the non-standard built-in predicate block/3 in SWI-Prolog conditional on its availability (this predicate was removed in SWI-Prolog 5.9.9).

git-svn-id: 4c7b768bc2e2a56aa1c56b1b5a9454ba68342430@5320 ac9c905b-388a-4ddf-9b6a-4063a022bc57

LogtalkDotOrg/logtalk2,LogtalkDotOrg/logtalk2,LogtalkDotOrg/logtalk2,LogtalkDotOrg/logtalk2,LogtalkDotOrg/logtalk2