Add flag for _update() whether precense should be modified
Add flag for _update() whether precense should be modified

This is a bugfix for an very particular issue.

Here's what happens:

If we create() an FileLockEntry and then update() it, we are running
into a problem because update() calls _update() which changes the
precense status of a FileLockEntry.

Because update() is _consuming_, the FileLockEntry gets drop()ed
afterwards. This _again_ causes _update() to be called, but with a new
presence status, which is not true in this moment (as the FileLockEntry
is still borrowed, but we already marked it as present).

This patch is a short-term fix. The real problem is, that our Store
interface is consuming. If the Store interface would be non-consuming,
this issue wouldn't happen, as the drop() call would not happen.

I'm rather sure that this patch will not be reverted in the process of
rewriting the Store interface to be non-consuming. But we never know.

mario-kr/imag,matthiasbeyer/imag,mario-kr/imag,matthiasbeyer/imag