Wrong instructions for removing old files during an update

[nuxwin]

Currently, all files INSTALL specify the wrong commands for deleting old files.

This is problematic for the following reasons:

1. Update broken due to the new SquirrelMail version integrated in 1.0.5:

The update instructions are wrong because the cp command can't override (replace) the -ReleaseNotes directory (that is provided by older versions of SquirrelMail) by the -ReleaseNotes file provided by the new SquirrelMail version.

2. Files that are not provided by the new ispCP package:

With the current deletion command, all files that are not provided by the new package are not deleted during update.

Conclusion:

To fix this two issues, we must just save configuration files and users data. All other files should be deleted.

[nuxwin]

Should be review due to the possible user personal components added into the ispCP docroot.

Thank to Benedikt for this issue.

[nuxwin]

Added (AGAIN) in r2689