Better 'is_permutation' implementation, tests

svn path=/trunk/boost/algorithm/; revision=84389
Added docs for C++14 variants of 'equal' and 'mismatch'

svn path=/trunk/libs/algorithm/; revision=84447
fixed Doxygen comment

svn path=/trunk/boost/algorithm/; revision=84448
Added documentation for 'is_permutation'

svn path=/trunk/libs/algorithm/; revision=84538