The printGPSCoords() function returns a copied C-style string. Since
the owndership is transferred to the caller, the correct return type
is "char *" instead of "const char *".
Thus a number of casts when calling free can be removed.
Moreover a number of callers didn't free the string and thus were
leaking memory. Fix them. Ultimately we might want two versions
of the function: one for QString, one for C-style strings.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>