Ann: SWI-Prolog 6.0.0

Hi,

I have uploaded SWI-Prolog 6.0.0. Bumping the major version to 6 is a
rather arbitrary choice in a project that works with a frequent
release cycle. The changes since 5.0 certainly justify it. I think
that just-in-time multi-argument indexing is nice execuse for a major
version step.

The list of changes is far too long to post here. Some highlights:

* Just-in-time hash-based indexing on any (and multiple) arguments.
* Abstraction of many of the development environment APIs to support
PDT (http://sewiki.iai.uni-bonn.de/research/pdt/start), an Eclipse
based IDE.
* Lots of portability and stability work. Experimental compilation
on MinGW (Windows). Many MacOS port issues (including support for
all current compilers: native gcc, gcc-llvm and clang).
* Enhancements to the development environment.
* Enhancements for generating executables (better tracking of undefined
references; include shared objects into the saved-state).

Enjoy --- Jan