Function: dbg_x
Section: programming/control
C-Name: dbgGEN
Prototype: vGD-1,L,
Help: dbg_x(A,{n}): print inner structure of A, complete if n is omitted, up to
 level n otherwise. Intended for debugging.
Doc: Print the inner structure of $A$, complete if $n$ is omitted, up
 to level $n$ otherwise. This function is useful for debugging. It is similar
 to \b{x} but does not require $A$ to be a history entry. In particular,
 it can be used in the break loop.
