Fix case sensitivity in recipient hash comparison

[fixes #501]

Previously the hash comparison was done on directly using the equality
operator. This proved to be too restrictive as hash implementations can
generate output of varying case. I changed the implementation so that
the generated hash and the expected hash are normalized to lowercase
before comparing.
Add test for lowercase hashes as well.
Fix test title
Merge pull request #502 from brianloveswords/501-case-insensitive-hashes

Fix case sensitivity in recipient hash comparison