currently 'configure', with no arguments, fails on the Mac because NTL compiles
itself for 64 bit, incompatibly.

1) control what NTL does, somehow

2) it should be easy to select 32 or 64 bit compilation with 'configure'.

3) make disable-fc-lib-ldflags the default on Mac, because with veclib
framework we don't need fortran libraries, and we get these annoying
messages:
    ld: warning in /usr/local/lib/gcc/i686-apple-darwin8/4.2.3/libgfortranbegin.a, file is not of required architecture
    ld: warning in /usr/local/lib/gcc/i686-apple-darwin8/4.2.3/libgcc.a, file is not of required architecture
