Some changes to configure.ac:

Some changes to configure.ac:

1. Includes BOOST_CPPFLAGS during compilation of all files, not just portfolio-relevant files.  This is necessary since we now have a general dependence on Boost (not just its threading stuff).  This resolves bug 357.

2. Support --disable-thread-support and --enable-thread-support, in an effort to get to the bottom of bug 361.

These changes shouldn't affect performance, though #1 will build the cvc4 libs with a couple of pthread definitions that conceivably could change the behavior of #included standard headers.  Let's keep an eye on tonight's regressions.