V1.5

1. make gdb statically linked
2. Fix bug when version is not only digit: gmp-6.0.0a.tar.bz2 -> gmp-6.0.0 after extracting
3. Use latest zlib when linking binutils and gcc
4. CentOS4 porting: add MPFR_DISABLE_THD_SAFE and MAKEINFO
5. Update latest version in script after determining version