Fix case sensitivity bug with tree iterators

With the new code to make tree iterators support ignore_case,
there is a bug in setting the start entry for range bounded
iterators where memcmp was being used instead of strncasecmp.
This fixes that and expands the tree iterator test to cover
the cases that were broken.
Merge pull request #1269 from arrbee/tree-iterator-case-sensitivity-bug

Fix case sensitivity bug with tree iterators