Content-Type header check is not case insensitive, again

[noresistence]

This is the same Issue as #10.

It has been fixed in branch 1.x-dev, but the fix has not been applied to branch 2.0-dev which appears to be the branch that is included in current joomla releases.

Quick summary:
Treatment of Headers does not respect case-insensitivity of HTTP Headers as of RFC 2616.

E.g. when checking the Content-Type header, this could just as well be named CONTENT-TYPE or content-type.

Please apply the fix also to current development branch and release a version that includes the fix.

It stops us from being able to upgrade Joomla without manually tweaking this problem.