Make concat work with special characters

Concat used to break badly with filenames or resource names containing
active shell characters such as question marks or asterisks.

Change the name of the fragment directory to the sha1 hash of the target
filename, thus avoid having to deal with special characters in most
places.

Use more resilient methods for enumerating files in concatfragments.sh.
This should allow arbitrary filenames only limited by the filesystem.
Add a test for special characters in filenames

Create a few fragments and files with difficult characters in their
names.