[R66] the file watcher regex are tested only against a full path

[bcarlin]

Originally, the regex filtering in the filewatcher was only able to match filenames.
In recursive mode, it was impossible to math a subpath.

During the 3.1 development cycle, I pushed some changes to match full paths. However, this had the side-effect to only allow file matching if the regex started with .* to match the subpath (ex: .*.csv). I.e. the regex myfile\.txt whould not match subpath/myfile.txt.

This PR allows both regex to work as expected:

• myfile\.txt matches myfile.txt as well as subpath/myfile.txt
• subdir/.+\.txt matches subdir/myfile.txt

[bcarlin]

@fredericBregier I think its ready!

[fredericBregier]

Fine for me