Remove dummy instances of Graph when plplot fixes the underlying problem

[Jari Häkkinen]

plplot is using dynamic loading and unloading of plot drivers. This works for several of the drivers but fails with the cairo driver. The plplot cairo drivers is actually using pangocairo and pangocairo does not support dynamic loading and unloading of runtime libraries (dynamic laoding only). I have reported my findings in the plplot issue tracking system, ​http://sourceforge.net/tracker/?func=detail&aid=3009045&group_id=2915&atid=102915

This ticket is inherited from ticket:469 where the work around was added. Simply remove the work around in bin/svndigest.cc and test/graph_test.cc when plplot fixes their bug.

[Jari Häkkinen]

(In [1170]) Fixes #469 and addresses #472. Work around for problem with multiple plot generation using pango.

[Peter Johansson]

The issue has been fixed upstream (2011-09-07) and should have been included in v5.9.9 (released Oct 2011).

[Jari Häkkinen]

Plplot v5.10.0 was released in February 2014 and with v5.10.0 we can remove the kludge introduced above. This means that we have to set the plplot requirement to 5.10.0 but I don't think this is a real issue since most package maintainers have included 5.10.0 into their distros. Also the 5.9.x line of plplot was really a development branch.

[Jari Häkkinen]

(In [1573]) Fixes #472. Removed workaround needed for plplot prior to 5.10.0