Add missing log categories

This is to fix superfluous log messages in custom logs. It adds categories to those JLog::add calls where there was no category specified yet.

Short history (tl;dr: skip this paragraph): For my own extension, I wanted to create a separate logfile.
For that reason, I called the addLogger function just as described here: http://docs.joomla.org/Using_JLog. I noticed however that some unrelated messages were cropping up from time to time in the extension's log files ("FinderIndexerAdapter::getTypeId", "Can't identify browser version. [..]"); that was even though I had specified my extension's name as category. Looking through the core code, I realized this was due those error messages not having assigned a proper category. That's why I've prepared this pull request for Joomla.

This is my first pull request for Joomla, so please point me in the right direction if there's anything amiss; I've already signed the contributor's agreement (my name is Bernhard Fröhler).

I hope I have chosen the correct branch to base this on - not sure about the branching strategy of Joomla? Are such fixes supposed to go into master first maybe? Problem is some things ("Can't identify browser") were already removed there. And which branches would this need to be merged in addition? I suppose 3.4-dev? Thanks in advance for your patience with a newbie...