Cannot use "." as file_observer output directory

[kyllingstad]

The constructor expression file_observer(".") — which is a quite natural way to say store output in the current directory — throws an exception with the following message:

boost::filesystem::create_directories: Invalid argument

Presumably, this is because create_directories() won't create a directory named ".".

I can see two different ways to fix this:

• Check whether the directory already exists using boost::filesystem::exists() before attempting to create it.
• Make the directory name absolute using boost::filesystem::absolute() before passing it to create_directories().