Fix quoted strings being parsed as booleans

[SPGoding]

parseBoolean() in StringReader parses certain quoted strings (e.g. "true", 'false') as booleans, which is pretty weird.

This PR trys to fix this and adds a test for it.

[msftclas]

All CLA requirements met.

[liach]

It's 1.16 update time, @Dinnerbone please reconsider looking into this (given fry is looking into DFU fixes).