Log Message:
Changes 3.1.2:
* Correct bug in configure script: --enable-portable-binary option was ignored!
* Threads compilation fix on AIX: prefer xlc_r to cc_r, and don't use
  either if we are using gcc.
* Updated FAQ to note that Apple gcc 4.0.1 on MacOS/Intel is broken,
  and suggest a workaround.  configure script now detects Core/Duo arch.
* Use -maltivec when checking for altivec.h.