add is_a_matrix (equivalent to is_a<matrix>) in ginac contrib : avoid a crash due to a dynamic_cast with macport/clang (I don't understand why but it's work if dynamic_cast is done in ginac src and not in feel src
up ginac (avoid crash with dynamic_cast ):
 - replace is_a<lst>(e) by e.info(info_flags::list) : equivalent -> see ginac doc
 - replace is_a<matrix> by is_a_matrix
minor up