arrayp() - determine whether or not a given variable is an
array
int arrayp( mixed arg );
Return 1 if `arg' is an array.
mapp(3), stringp(3), objectp(3), intp(3), bufferp(3),
floatp(3), functionp(3), nullp(3), undefinedp(3),
errorp(3), pointerp(3)