Add index version of preprocess_sparse_table().
Doc changes, concept specifications.
Add concept assertions to LCA.
Add cycle_detector dfs visitor.
Add some concept checks to graph visitors.
Remove superfluous collection size check.
Add Boost concept assertions.
Change from BOOST_CONCEPT_REQUIRES to BOOST_CONCEPT_ASSERT.
Add doxygen comments.
Add lca_query (not working yet).
Add representative_element() that outputs array indices.
Add index data to the fixture.
Removed broken representative_element functions; fixed array version.
Updated LCA and tests accordingly.