Fix graph_parallel test conversion from const optional<> to
a non-const bool.
Remove unused variables

This fixes compiler warnings about variable shadowing.
Merge pull request #11 from MarcelRaad/patch-1

Remove unused variables

Tested with clang-5.1 on Mavericks, thanks Marcel.
Fixed bug 10222.
Fixed bug 10231 partly: If finish_edge was called, then now correctly.

The bug that it never gets called with the current construction remains.
Merge branches 'bugfix/ticket-10222-root-map-broken' and 'bugfix/ticket-10231-dfs-never-calls-finish_edge' into develop
Added support for an finish_tree_edge event in depth_first_search.