Keep size of regular expressions below 32 kbyte.

* gentoo-syntax.el (ebuild-mode-collect-equal-cdrs): New optional
argument LIMIT starts a new element in the destination list, after
that number of elements from the source list have been collected.
(ebuild-mode-font-lock-keywords): Limit regexp size by calling
ebuild-mode-collect-equal-cdrs with the limit argument; a value
of 1000 appears to keep the size is below the 32 kbyte limit.
See also the change of 2012-09-22.
Update copyright years.