bug#21271: 25.0.5; `field' text-property screws with `line-end-position'

[Drew Adams]

Confirmed.  This is the case as far back as property `field' has
existed, AFAICT.  (It is not the case for Emacs 20, which has no
built-in property `field'.  It is the case for Emacs 22.  Dunno
about 21.)

But this part of the doc string seems to indicate that this behavior
is to be expected:

 This function constrains the returned position to the current field
 unless that would be on a different line than the original,
 unconstrained result.  If N is nil or 1, and a rear-sticky field ends
 at point, the scan stops as soon as it starts.  To ignore field
 boundaries bind ‘inhibit-field-text-motion’ to t.

> 1. In an empty buffer, hit RET and type some text on the second
> line.
> 2. Place point at the start of the second line.
> 3. Run (line-end-position) and verify that the value is correct
> (something greater than 3)
> 4. Run (add-text-properties (1- (point)) (point) '(field 1))
> 5. Run (line-end-position) and you'll get 2 (which is the poistion
> of the end of the field).