Add XeTeX for document building

Add XeTeX for document building

Prefer XeTeX than pdfTeX.

Discussion:
http://lists.gnu.org/archive/html/lilypond-devel/2015-12/msg00136.html
http://lists.gnu.org/archive/html/lilypond-devel/2016-01/msg00041.html

*** This patch requires Issue 4735. ***
https://sourceforge.net/p/testlilyissues/issues/4735/

[lemzwerg, 2016-01-10 09:29:42]

LGTM

[trueroad, 2016-01-12 14:34:37]

texinfo.tex's XeTeX support seems have still some issues.

Here's LilyPond PDF documents generated by XeTeX.
https://drive.google.com/file/d/0ByGBX3PDrqjsQmllOXBUQW1rbkU/view?usp=sharing

I've noticed that non-ascii characters of ``Table of Contents'' are broken.
Would you review XeTeX generated documents and find other problems?

I'll change Issue 4735, 4736 and 4737 patch status to needs_work.
I won't change status of Issue 4729, 4731, 4732, 4733 and 4734 because they are
no problem.

Already, I've reported the broken TOC issue to bug-texinfo.
http://lists.gnu.org/archive/html/bug-texinfo/2016-01/msg00067.html

It is able to be resolved in LuaTeX.
http://lists.gnu.org/archive/html/bug-texinfo/2016-01/msg00069.html

However, we cannot use LuaTeX that still has another issue.
http://lists.gnu.org/archive/html/bug-texinfo/2016-01/msg00056.html
http://lists.gnu.org/archive/html/bug-texinfo/2016-01/msg00055.html

On the other hands, in XeTeX, it is difficult to solve the broken TOC issue in a
similar way as LuaTeX.
http://lists.gnu.org/archive/html/bug-texinfo/2016-01/msg00070.html
http://lists.gnu.org/archive/html/bug-texinfo/2016-01/msg00071.html

I've created a texinfo.tex's patch for the broken TOC issue in other ways.
http://lists.gnu.org/archive/html/bug-texinfo/2016-01/msg00072.html
http://lists.gnu.org/archive/html/bug-texinfo/2016-01/msg00073.html

[trueroad, 2016-02-09 14:51:48]

All required patches are merged into Texinfo.

Texinfo update is Issue 4735.
So this patch requires Issue 4735. 
https://sourceforge.net/p/testlilyissues/issues/4735/

[trueroad, 2016-02-09 15:01:54]

Here's LilyPond PDF documents generated by XeTeX in my environment.
https://drive.google.com/file/d/0ByGBX3PDrqjsZkF1VHFqakZqSGM/view?usp=sharing

[trueroad, 2016-02-27 14:25:08]

I've pushed to staging.


Issue 4737: Add XeTeX for document building

author    Masamichi Hosoda <trueroad@trueroad.jp>
          Sat, 9 Jan 2016 18:12:41 +0000 (03:12 +0900)
committer Masamichi Hosoda <trueroad@trueroad.jp>
          Sat, 27 Feb 2016 14:22:17 +0000 (23:22 +0900)
commit    424be60367b0546e4e57307dccf1ba0d9488044c