Bug 890896 - Prediction capitalization gives different scores when capitalize is true

Fix for [#890896](https://bugzilla.mozilla.org/show_bug.cgi?id=890896). We give different results back at the moment if the first character is a capital. I don't think we should do that, because in 99% of the case the capital is not selected by the user but rather the result of auto-capitalization. In this patch we'll always look for the lowercase version of the word so we get the same results in both cases.