BEAUtii Link/unlink of tree partitions can fail

[rbouckaert]

When a partition name is the postfix of another partition name, and when linking the postfix is the name of the linked partition it can happen that after unlinking the IDs of unlinked objects becomes mangled. For example, having a coding and noncoding partition may result in IDs of the form nonnoncodig. This results in duplicate tree priors.
To fix this, the method BeautiDoc.renameId should be robustified.