fix for handling of password store items with children

Hi,

I was not able to get the plugin to work with password store items which contain children, such as the following:

foo.com
\\--- pass @p4ssw0rd!
\\--- login myusername

I believe there is a problem with the way bestFitItem is being calculated. In the above example, bestFitItem was being set to `pass` rather than `foo.com`. I have tested a fix locally on firefox 24.4 on linux.

The first commit also separates the logic for hierarchical- vs multiline-style nodes in getPasswordData(). This might not be strictly necessary, but I don't think there is a case where both logic paths would be applicable.

Thanks & hope you find this useful.

-fishyfriend