precompiled jam executables uploaded

I just uploaded precompiled jam executables to the Files section for linuxx86, irix and solaris. I also added an InstallingBoost page to the Wiki with links to these executables. I hope this helps people with using the Boost.Build system. I gzip'ed the executables (except for the linux one) since I'm not sure if users find it a hassle to gunzip them first. It would safe space in the Files section though. People with jam executables for other platforms, please add them or transfer them to me so I can put them on there. toon