tigefa4u projects Trac

`trac.util` is now a package. Split out `Markup` class into separate `trac.util.html` module.

Add two methods to the `Markup` class:
`stripentities(keepxmlentities=False)`:: Replaces all character or numeric entities in the text with equivalent UTF-8 characters, optionally keeping the core XML named entities in place.
`plaintext(keeplinesbreaks=True)`:: Strip all tags and entities from the text, and optionally also replace line breaks with regular spaces (replacing the `rss_title` method).

Correctly highlight a search term prefixed by a "!" character. Closes #2718.

A few typos fixes contributed by Andres Salomon, thanks!

Closes #2813 and #2822.

Improve TracRevisionLog textual !ChangeLog format (3/3): Adding ''action'' information to the output

Improve TracRevisionLog textual !ChangeLog format (2/3): Move the information specific to the changelog format out of the generic `get_changes` function.

Improve TracRevisionLog textual !ChangeLog format (1/3): Refactoring log_changelog.cs to use the ClearSilver ''with'' command.

Ported [2969] to 0.9-stable (fixing #2777).

Gracefully handle invalid character entities in verbatim HTML. Closes #2777.

Autodetect big changesets and optimize their display.

When a changeset is deemed to be too big to be displayed in one page containing all the diffs, the actual diffs are simply not included in the view.

Instead, the modified file entries have a link pointing to a TracChangeset view that will contain only the changes affecting that file.

In order to detect big changesets, the following heuristic is used:
1. The sum of the sizes in bytes of the modified files (old ones + new ones) should not exceed the `max_diff_bytes` parameter
2. The total number of files in the changeset should not exceed the `max_diff_files` parameter.
3. If there's only one file modified, rule 1. is ignored and the diff content is always shown.

The following defaults are used:
{{{
[changeset]
max_diff_bytes = 10000000
max_diff_files = 1000
}}}

This should close #2343 and #2591.