#787 Needbased backup calculates checksums of dirty files

[Stefan Rossbach]

The backup feature calculates the file checksum directly from the file. This is wrong if an open editor for this file exists
and was already edited and so may replace unsaved content because the logic do not ask the user if the file content (checksums)
matches and just replace the file.

[Stefan Rossbach]

Steps to reproduce:

Create two files.

Do a full sharing. After the synchronization had finished stop the session.

Now do a partial sharing and only share one of those files.

On the client side edit the non shared file but do NOT save it.

Switch to host side and enable the Needbased Feature.

Start editing the non shared file.

On the client side an ECLIPSE !!! (nothing from Saros) dialog is opened that asks you to
save the file (because the Saros Logic tries to close the editor).

It does not matter which button you pressed, the file gets overwritten
and the old content is lost.

[Stefan Rossbach]

333aefe8810fd12bbf80c6df2d13804d512c9c13