Auto insertion of ampersands.

* latex.el: Enhance array and tabular(*) environments support.
(LaTeX-env-array): Add call to `LaTeX-item-array'.
(LaTeX-env-tabular*): Add call to `LaTeX-item-tabular*'.
(LaTeX-array-skipping-regexp): New variable.
(LaTeX-tabular*-skipping-regexp): Ditto.
(LaTeX-item-array): New function.  Put line break macro on the
last line and insert suitable number of ampersands.
(LaTeX-item-tabular*): Ditto.
(LaTeX-insert-ampersands): New function.  Insert suitable number
of ampersands.
(LaTeX-array-column-letters): New variable.  Column letters for
array-like environments.
(LaTeX-array-count-columns): New function.  Count number of
ampersands to be inserted.
(LaTeX-common-initialization): Add entries to LaTeX-item-list to
use `LaTeX-item-array' and `LaTeX-item-tabular*'.

* style/amsmath.el: Enhance alignat-like environments support
as well as some cleanups.
(LaTeX-item-equation-alignat): New function.  Insert contents to
terminate a line in multi-line equations environment.
(LaTeX-amsmath-env-alignat): Use it.  Add doc string.
(LaTeX-amsmath-env-alignedat): Ditto.
(LaTeX-amsmath-env-aligned): Removed.  Just specifying a prompt
string for an optional argument is enough.
(LaTeX-item-equation): Take over the job of
`LaTeX-item-equations'.  Add an optional `suppress' argument:
when it is non-nil skip putting line break macro.  Add doc string.
(LaTeX-item-equations): Removed.  Its task is now covered by
`LaTeX-item-equation'.
(LaTeX-item-equation-alignat): New function.  Insert ampersands
according to the columns number, as well as calling
`LaTeX-item-equation'.
(LaTeX-amsmath-alignat-number-of-ampersands): New function.
("amsmath"): Arrange setups of variables to adopt the above
changes.

* style/array.el ("array"): Change `LaTeX-array-column-letters'
locally to include addtional letters extended in array.sty.

* style/plext.el: New style file.  Add support for extended
format for array-like environments.

* Makefile.in (STYLESRC): Include style/plext.el.

* doc/auctex.texi: Add documentation for the above enhancements.

* doc/changes.texi: Ditto.

Signed-off-by: Mosè Giordano <mose@gnu.org>
Remove .cvsignore and tests from the release tarball.

* Makefile.in: Update copyright years.
(EXCLUDEDFILES): Rename from GITFILES.  Remove also .cvsignore and
tests from the release tarball.
(release-commit): More precise suggestion to push tag and release
commit.
(tar-ball): Use EXCLUDEDFILES in place of GITFILES.