added sha1 tests for really long messages

svn path=/branches/release/libs/uuid/; revision=80502
seed_rng.hpp - removed incorrect comment
seed_rng.hpp - used ignore_size() to get rid of warnings
seed_rng.hpp - initialize m_value in generator_iterator constructor
sha1.hpp - added #include <string> as std::runtime_error constructor needs it

svn path=/branches/release/boost/uuid/; revision=80846
fixed bug in sha1.hpp for messages longer than 536,870,912 bytes, ticket #7128

svn path=/branches/release/boost/uuid/; revision=80954