[boost] [preprocessor] More changes for Digital Mars, and some of the examples.

Hello, I've got some more changes for the preprocessor library. I noticed the other day that there are no tests for sequences in the preprocessor library, which meant that I hadn't tested them on Digital Mars, so I missed a couple of changes that were needed there. I've put up a patch at: http://myweb.tiscali.co.uk/calamity/patches/preprocessor-2.patch.gz This also contains some unit tests for sequences (I just took the list tests and made some changes). It also fixes some typos in the examples in the reference documentation. Daniel