Merge branch 'issue-6' into 'master'

fix: correct handling of HttpServletRequest#getHeaders and tests

This pull request addresses issue #6.

Properly handles cases where container may return blank String values in the returned list. 
Tests were previously adding List objects as headers - need to add just String values.

See [the javadocs for HttpServletRequest#getHeaders](http://docs.oracle.com/javaee/6/api/javax/servlet/http/HttpServletRequest.html#getHeaders(java.lang.String)) for reference.
 
I intend to release 1.6.1 when this is merged.

Edit: this also corrects the case of the name of the Manifest `isMemberOf` header.

cc: @paul.erickson @levett @bhill6 

See merge request !23