[Bug-gnubg] one (picky) warning

[Joseph Heled]

If we want to be extra picky, I still get one warning

gnubg.c:7639: warning: passing arg 2 of `iconv' from incompatible 
pointer type

Now, configure said it groked my proto as:

   extern size_t iconv (iconv_t cd, char * *inbuf, size_t *inbytesleft, 
char * *outbuf, size_t *outbytesleft);

So what irkes the compiler is the extra const in 'const char ** inbuf'

A quick look at the configure script showed it need to be replaced by 
ICONV_CONST.

Fixed in development branch.

-Joseph