Disjunct_struct: Change union order for portability
Disjunct_struct: Change union order for portability

The code depends on is_category and num_categories to use identical
memory location. This would get violated if sizeof(int)!=sizeof(float)
or sizeof(char *)!=sizeof(Category_cost *).

Fixed by staring with is_category and num_categories, so they are
guaranteed to use the same memory.

opencog/link-grammar,opencog/link-grammar,linas/link-grammar,linas/link-grammar,ampli/link-grammar,opencog/link-grammar,ampli/link-grammar,ampli/link-grammar,opencog/link-grammar,ampli/link-grammar,linas/link-grammar,opencog/link-grammar,ampli/link-grammar,opencog/link-grammar,linas/link-grammar,ampli/link-grammar,linas/link-grammar,linas/link-grammar,linas/link-grammar,opencog/link-grammar,ampli/link-grammar,ampli/link-grammar,linas/link-grammar,linas/link-grammar,opencog/link-grammar,ampli/link-grammar,opencog/link-grammar