Merge units from trunk

svn path=/branches/release/boost/units/; revision=65898
Merge fixes for test_output from the trunk.

svn path=/branches/release/libs/units/; revision=68625
Merge units from the trunk.

svn path=/branches/release/boost/units/; revision=71383
Merge units from the trunk.

svn path=/branches/release/boost/units/; revision=78342