use readlink(1) on each file that we think is different to ensure that
only the resolved path is included

ok ajacoutot@, tb@

Add a comment about why we need to ignore the timestamps on perl man pages
(Pod::Man adds the current date to the manuals).

ok robert@

Catch non existent files (in case a syspatch would _add_ a new file).

do not remove used files from the fakeroot

do not leave temp files after the diffing is done

Add a small shell script to be used by syspatch to diff the fake root
directories for changes due to the fact that we have to do some "magic"
to figure out if things have really changed.