bug#15797: 24.3.50; Info: Mention cache-long-scans

[Jambunathan K]

NEWS file seems to be lying wrt `cache-long-line-scans' or
`cache-long-scans'.  I see no entry for these in the manual.

Temporary note:
+++ indicates that all necessary updates to the manuals in doc/ are complete.


+++
** `cache-long-line-scans' has been renamed to `cache-long-scans'
because it affects caching of paragraph scanning results as well.

----------------------------------------------------------------

In GNU Emacs 24.3.50.4 (i686-pc-linux-gnu, GTK+ Version 2.20.1)
 of 2013-10-30 on debian-6.05
Bzr revision: 114868 rgm@gnu.org-20131030102316-8vif7u6ecyo3yieg
Windowing system distributor `The X.Org Foundation', version 11.0.10707000
System Description:     Debian GNU/Linux 6.0.5 (squeeze)