Split suggestName(); the split method doesn't check if file exists

The idea is that e.g. KIO can use suggestNameOnly() to get a new file/dir name then use a StatJob of some kind to check whether the newly suggested name alreayd exists or not and adjust accordingly.

This also gets rid of the recursion that existed in suggetName() calling itself, now it can just call the new method.

For more details see kio!153 (merged)