STLplus C++ library collection SVN stlplus3

Reworked the path_exists algorithm. The algorithm was giving up the
search too soon in the case when one arc went to a visited node,
sibling arcs didn't get visited. I have rewritten the algorithm
completely using a simpler method. Also changed the test pack to
compare the output of the path_exists algorithm with the all_paths algorithm.

replaced digraph::clear with a more efficient implementation - this is called from many places including the destructor

minor edit incorrect message, added extra progress check

Synchronised with source code

Replaced the simple_ptr with DJDM's latest update with deferred
allocation of the alias count - now working in Visual Studio. Also
slight mod to test to avoid trying to pass a temporary by reference.

Optimised by DJDM such that a reference count of 1 is represented by a
missing counter (i.e. null counter pointer). This eliminates many
counter allocations and deallocations.

Optimised by DJDM such that a reference count of 1 is represented by a
missing counter (i.e. null counter pointer). This eliminates many
counter allocations and deallocations.

Summary: Fixed bug introduced by the lkast bug fix whereby simplify is
not always called on paths which are generated using
initialise_folder. I have reinstated path simplification in
initialise_folder. This means that there are now some scenarios where
simplify is called twice but at least it is now functionally correct.

Incremented version for these changes

updated documentation to match code changes