[Bug-apl] API for GNU APL

[Dirk Laurie]

Hi Jürgen:

I've got code that works except for bugs unconnected with the GNU APL
routines.

I decided to implement the interface as a wrapper for an item of type
`const Value_P&`. API.cc contains the following lines:

// The commented-out variants give segmentation errors, I don't understand why.
// Maybe needed only when `value` is Value*. not when it is already Value_P.
// Jürgen will know.
// #define PCLONE(valuep) valuep
// #define PCLONE(valuep) Value_P(valuep)
#define PCLONE(valuep) *(new Value_P(valuep))

I.e. instead of initializing the item as e.g. `symbol->get_value()`,
I initialize it as `PCLONE(symbol->get_value())`.

I have not laboriously checked in which places this additional `new`
is really necessary, all I know is that it is necessary for at least one
of them.

Best wishes
Dirk