Fix a "pointer type missmatch" warning.

Fix a "pointer type missmatch" warning.

In particular, the second parameter in the call to iconv() will
cause this warning if your library declares iconv() with the
second (input buffer pointer) parameter of type const char **.
This is the old prototype, which is none-the-less used by the
current version of newlib on Cygwin. (It appears in old versions
of glibc too).

Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Junio C Hamano <junkio@cox.net>