COMMON: Make use of ICONV_CONST

Is #define'd "const" if the iconv() implementation is of type
size_t iconv(iconv_t, const char **, size_t, char **, size_t)
instead of
size_t iconv(iconv_t, char **, size_t, char **, size_t).

This is apparently the case for FreeBSD and PPC-based Mac OS X.
COMMON: Add "LL" to another big integer constant