[boost] [mpl] Updated fixes on 'master'

A number of fixes in mpl, by Bruno Dutra and Deniz Bahadir, had been tested on 'develop' for quite a long time but had not been merged to 'master' for the upcoming release. The regression tests on 'develop' had shown that the fixes were working properly and I have taken the responsibility of merging them now to 'master' for the upcoming release. I will be checking the 'master' regression tests. If there are any problems I will revert this merge but I am 99.99% certain that the changes are correct, so I take full responsibility for merging. The fixes come from Trac items so I feel that correcting these bugs is important for the upcoming release else I would not have performed the merge and the push to Boost.