Fix LDAP attribute case sensitivity issue

[dfanara]

Fixes an issue described in #1317 where attributes with upper-cased characters were not mapped correctly.

[ssddanbrown]

Thanks for this @dfanara.

Just one question, I understand that the casing will need to be lowercase for accessing the response from the LDAP query but I see this change will also lower-case the attribute in the query itself. Will that be an issue?

Just wondering if it would safer to leave the casing for the query and convert to lower-case only when reading the result (In the getUserResponseProperty function maybe).

[ssddanbrown]

As of this change I believe this pull request is now redundant.

Thanks again @dfanara for offering this pull request.