when=XXX did work already. This patch allow to write this with spaces around the
equal sign - as in every other backup.d/ file.

The modelines added match the emacs lines already present and also set
the filetype to sh (just like the emacs lines).

Previously, there were many indentation styles in use: Real tabs, 2, 3
or 4 spaces, mixing these within the same file, function or even within
a single line.

This commit changes all bash scripts in the handlers, src and lib dirs
to use consistent indentation: three spaces are now used everywhere.
Other files (e.g. Makefiles) are left untouched.

Additionally, this commit removes all trailing whitespace.

 Reverted indentation level to 3.

 Changed default indentation level to 8, to make it presbyopia-friendly