Doc changes for cache-long-scans

Ref: http://debbugs.gnu.org/15797#65

* doc/lispref/display.texi (Truncation):
* doc/lispref/positions.texi (Screen Lines): Do not mention cache-long-scans.

* src/buffer.c (cache-long-scans): Doc fix.

* etc/NEWS: Related edit.

1 files changed, 2 insertions, 2 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 7f58284d978..ea2287e0f5e 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -240,9 +240,9 @@ to be printed in other formats (octal, hexadecimal, and character).
 ** `write-region-inhibit-fsync' now defaults to t in batch mode.
 
 +++
-** `cache-long-line-scans' has been renamed to `cache-long-scans'
+** `cache-long-line-scans' is now non-nil, and renamed to `cache-long-scans',
 because it affects caching of paragraph scanning results as well.
-Also, it is now enabled by default.
+There is no reason to set this to nil except for debugging purposes.
 
 ---
 ** The option `set-mark-default-inactive' has been deleted.