Add indentation for tabular environment.

* latex.el: `LaTeX-indent-tabular' now indents tabular-like environments.
  (LaTeX--tabular-like-end): new variable.
  (LaTeX-indent-environment-list): added `LaTeX-indent-tabular' as
  indenter for "tabular" and "align", added a setter that recomputes
  `LaTeX--tabular-like-end'
  (LaTeX-env-beginning-pos-col): new function.
  (LaTeX-hanging-ampersand-position): new function.
  (LaTeX-indent-tabular): new function.

* tests/latex/latex-test.el : added an ERT test for `LaTeX-indent-tabular'
  (LaTeX-indent-tabular-test/in): input filename variable
  (LaTeX-indent-tabular-test/out): output filename variable

* tests/latex/tabular-in.tex: input to latex-test.el

* tests/latex/tabular-out.tex: input to latex-test.el

* tex.el (TeX-how-many): added for compatibility with XEmacs.

Signed-off-by: Tassilo Horn <tsdh@gnu.org>
Use enhanced tabular indentation for more envs.

* style/longtable.el ("longtable"): Use `LaTeX-indent-tabular'
also for longtable environment.

* style/tabularx.el ("tabularx"): Use `LaTeX-indent-tabular' also
for tabularx environment.

* style/tabulary.el ("tabulary"): Use `LaTeX-indent-tabular' also
for tabulary environment.

* latex.el (LaTeX-indent-environment-list): Use
`LaTeX-indent-tabular' also for array and eqnarray environments.
Mention new tabular indentation in changes.texi.

* doc/changes.texi: Mention the enhanced tabular indentation.