Make the sample-vs-cylinder pressure check more liberal

Make the sample-vs-cylinder pressure check more liberal

This makes it consider them to be identical if they are within half a
bar of each other.  If you edit the pressures by hand and set them to
the same bar pressure as the samples, they may not be identical to the
last milli-bar, but clearly the manually entered cylinder pressure isn't
significantly different from the sample data, so consider it redundant.

We do want manual overrides of cylinder pressures to take precedence
over sample data (as Dirk so eloquently puts it, some dive computers
really don't have very reliable sample data), but at the same time the
sample data is the one we are expecting to be fairly accurate.  The
starting and ending pressure overrides are for when there is no sample
data, or when the sample data is totally wrong for some reason.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>