Added library for GT based clustering

git-svn-id: https://farsight-svn.ee.uh.edu/repos/farsight/trunk@4756 9053f808-4e3f-0410-9672-ef3bfcbbeb84
1. Added interface functions for computing tracing costs for Trace Editor. 2. Write segmentation mask as label image. 

git-svn-id: https://farsight-svn.ee.uh.edu/repos/farsight/trunk@4757 9053f808-4e3f-0410-9672-ef3bfcbbeb84
Added flags for GT clustering library.

git-svn-id: https://farsight-svn.ee.uh.edu/repos/farsight/trunk@4758 9053f808-4e3f-0410-9672-ef3bfcbbeb84
Added functions for auto-merging gaps. More functions for dealing with graphs.

git-svn-id: https://farsight-svn.ee.uh.edu/repos/farsight/trunk@4759 9053f808-4e3f-0410-9672-ef3bfcbbeb84
ENH: Add method to prune tree on smoothed graph to MRT

git-svn-id: https://farsight-svn.ee.uh.edu/repos/farsight/trunk@4760 9053f808-4e3f-0410-9672-ef3bfcbbeb84
Forgot to add some guards for vessel tracer

git-svn-id: https://farsight-svn.ee.uh.edu/repos/farsight/trunk@4761 9053f808-4e3f-0410-9672-ef3bfcbbeb84
Forgot to add some more guards for vessel tracer

git-svn-id: https://farsight-svn.ee.uh.edu/repos/farsight/trunk@4762 9053f808-4e3f-0410-9672-ef3bfcbbeb84