Comment 1 for bug 699264

I remove the older patch: it's signal handler invokes
non-async-signal-safe functions, which may be dangerous
for the system.

Furthermore, non-POSIX platforms may be actually
no safe possibility to save a file from a signal handler
(for example,
 http://msdn.microsoft.com/en-us/library/aa272921(VS.60).aspx:
 no system call allowed
).

In backups.bis.diff signal handling is switched with
--enable-signals configure option; it is disabled by default.
also, unsafe stuff is hopefully eliminated from the handler.

I tested a random board, it saves with date-only difference
relatively to the unpatched version, though a more thourough
test is probably needed: the patch is not very short.