bug#17207: 24.3; html-mode incorrect indentation inside template syntax

[Jon Dufresne <jon.dufresne@gmail.com>]

Create a test.html file. Use html-mode. Fill with the following
contents:

```
<table>
  <thead>
    <tr>
      {% for header in headers %}
	<th>{{ header.attr1 }}</th>
      <th>{{ header.attr2 }}</th>
      {% endfor %}
    </tr>
  </thead>
</table>
```

This is a mix of HTML and Django template syntax [0]. If you indent line
6 (<th>{{ header.attr2 }}</th>) I would expect the line to align itself
with the previous line (<th>{{ header.attr1 }}</th>). Instead it appears
to aligns itself with the "for" template tag or perhaps the <tr> plus an
offset. The final result after indenting line 6 is as it appears above.

The mode pony-tpl-mode [1] uses html-mode to calculate indentation when
then previous line looks like HTML and not special syntax. See my bug
report there: https://github.com/davidmiller/pony-mode/issues/81

[0] https://docs.djangoproject.com/en/dev/topics/templates/
[1] https://github.com/davidmiller/pony-mode


In GNU Emacs 24.3.1 (x86_64-redhat-linux-gnu, GTK+ Version 3.9.10)
 of 2013-08-14 on buildvm-17.phx2.fedoraproject.org
Windowing system distributor `Fedora Project', version 11.0.11404000
System Description:	Fedora release 20 (Heisenbug)

Configured using:
 `configure '--build=x86_64-redhat-linux-gnu'
 '--host=x86_64-redhat-linux-gnu' '--program-prefix='
 '--disable-dependency-tracking' '--prefix=/usr' '--exec-prefix=/usr'
 '--bindir=/usr/bin' '--sbindir=/usr/sbin' '--sysconfdir=/etc'
 '--datadir=/usr/share' '--includedir=/usr/include'
 '--libdir=/usr/lib64' '--libexecdir=/usr/libexec'
 '--localstatedir=/var' '--sharedstatedir=/var/lib'
 '--mandir=/usr/share/man' '--infodir=/usr/share/info' '--with-dbus'
 '--with-gif' '--with-jpeg' '--with-png' '--with-rsvg' '--with-tiff'
 '--with-xft' '--with-xpm' '--with-x-toolkit=gtk3' '--with-gpm=no'
 'build_alias=x86_64-redhat-linux-gnu'
 'host_alias=x86_64-redhat-linux-gnu' 'CFLAGS=-DMAIL_USE_LOCKF -O2 -g
 -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions
 -fstack-protector-strong --param=ssp-buffer-size=4
 -grecord-gcc-switches -m64 -mtune=generic' 'LDFLAGS=-Wl,-z,relro ''

Important settings:
  value of $LANG: en_US.utf8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: HTML

Minor modes in effect:
  tooltip-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
<down> <down> <down> <down> <down> <tab> M-x b u <tab> 
<backspace> <backspace> r e p o <tab> r <tab> <ret
urn>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
`flet' is an obsolete macro (as of 24.3); use either `cl-flet' or `cl-letf'.
Loading /home/jon/pony-mode/src/pony-tpl.el (source)...done
Loading vc-git...done
Making completion list... [2 times]

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None found.

Features:
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mail-prsvr mail-utils help-mode vc-git pony-mode easy-mmode edmacro
kmacro help-fns cl-macs gv which-func imenu sql thingatpt sgml-mode
python rx easymenu comint ring ansi-color files-x dired-aux dired cl
cl-lib time-date tooltip ediff-hook vc-hooks lisp-float-type mwheel
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newcomment lisp-mode register page menu-bar rfn-eshadow timer select
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georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
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