Remove generated html before generating a new version.
Fixed documentation flaw #7947, reported by Marvin Sielenkemper.
Made the data of identity_element static in order to avoid unnecessary default constructions.
Adaptations of some tests for gcc-4.7.1-c++11
Simplifying operator = implementations with move using call by value ("sink arguments").
Fixed ticket 8350 reported by Evgeny Panasyuk on 2013/03/29: closed_interval.hpp misses include of concept_check.hpp.