Instead of storing the full content twice when creating Difference objects, we
now directly run `diff` and store the unified diff. Large blocks in the diff
are still trimmed. This results in huge memory savings and debbindiff can now
happily compare changes for installation-guide.

As tool_required() is not only for comparators anymore, we move it to
debbindiff, together with logger.

Text output becomes really straightforward as we just have to write what
we've previously recorded.

For the HTML output, we stop using vim and instead borrow code from
diff2html.py found at <http://git.droids-corp.org/?p=diff2html.git>.

Closes: #772029
Closes: #779476

If different encodings are detected, compare_text_files will be given
encoding=None. Let's try to decode stuff as utf-8 as a best guess.
We'll fallback on binary comparison if that doesn't work out well.

Helmut Grohne authored Mar 26, 2015 and Jérémy Bobbio committed Mar 27, 2015

Make print_func accept unicode objects by opening the output using the
codecs module. This affects --html output.

Closes: #778641

Helmut Grohne authored Mar 26, 2015 and Mattia Rizzolo committed Mar 27, 2015

Example input package triggering the error: libreadline6

Example traceback being fixed:

Traceback (most recent call last):
  File "/usr/bin/debbindiff", line 120, in <module>
    sys.exit(main())
  File "/usr/bin/debbindiff", line 114, in main
    output_text(differences, print_func=print_func)
  File "/usr/lib/python2.7/dist-packages/debbindiff/presenters/text.py", line 71, in output_text
    print_details(difference, print_func)
  File "/usr/lib/python2.7/dist-packages/debbindiff/presenters/text.py", line 62, in print_details
    print_details(detail, new_print_func)
  File "/usr/lib/python2.7/dist-packages/debbindiff/presenters/text.py", line 62, in print_details
    print_details(detail, new_print_func)
  File "/usr/lib/python2.7/dist-packages/debbindiff/presenters/text.py", line 62, in print_details
    print_details(detail, new_print_func)
  File "/usr/lib/python2.7/dist-packages/debbindiff/presenters/text.py", line 59, in print_details
    print_difference(detail, print_func)
  File "/usr/lib/python2.7/dist-packages/debbindiff/presenters/text.py", line 36, in print_difference
    if not difference.lines2[-1].endswith('\n'):
IndexError: list index out of range

Closes: #779391

Closes: #778537

Closes: #779475

Closes: #779474

The `tool_required` decorator now raises an exception when
the command cannot be found. This enables more flexible handling.
Associated Debian package is now suggested in the comment.

The list of external tools is now available through the `--list-tools`
command-line option. We also use this output to generate the Recommends field.

Move the packages of those tools to Recommends section.

Comparing squashfs images could be interesting for
embedded Linux distributions like OpenWrt.

Added squashfs-tools only to Recommends, as it is
less relevant for Debian.

It only produces large diffs when file sizes
differ and has no real practical use.

This reverts commit d4dfb1f9.

Depends are not correctly generated anymore.