[PATCH 0 of 4] keyword: support rollback, handle diffs more gracefully

[Christian Ebert]

Hi,

The most important change in this series is the support of the
rollback command by the keyword extension (4th patch).

While not having an immediate effect on the repository itself, in
conjunction with the 3rd patch it improves the user experience by
eliminating more chances that spurious differences are presented
to the user.

The 3rd patch suppresses any expansion within a diff operation.
The main reason for expanding keywords when comparing with the
working directory was in fact to detect "wrong" expansions caused
by rollback.

The first 2 patches are minor fixes, the 2nd is a resend.

c