The templated provides an unary predicate for (shared) pointers that
allows containers containing pointers to objects to be searched, not by
pointer comparisons but by comparisons of the values that they point
to. This allows std::find_if to be used with shared pointers in a similar
manner that std::find is used with non-pointer objects.
The session command history is now compacted to contain only the first and
last execution of a session command. This should still allow most of the
more eccentric use-cases of user variables while keeping the session
command history smaller.
Added some convenience functions into the SessionCommand class to make the
pruning process easier.
Using the same implementation of the Backend and SessionCommand classes in
both schemarouter and readwritesplit will prevent duplication of code.
This commit only splits the generic parts of the class to a Backend class
which the schemarouter then extends. The session commands for both routers
are similar so they require no special handling.
