#36 Error when using nextool.pl to exclude a subtree

[Mikhail Bezruchko]

When using nextool.pl to exclude a subtree, 'Span' and 'History' blocks are not
updated properly.
To replicate the problem, use use PF00034_39.nex - a data set (cyto c) that has
tigriopus OTUs, and exclude the subtree defined by inode18:

$ nextool.pl PF00034_39.nex out.nex exclude subtree inode18

Open the out.nex file and:
- Check the 'Span' block -- you will find that tigriopus OTUs are still present.
- Check the 'History' block -- you will find that the node and OTUs are still
present in the tree.