tigefa4u projects Trac

Allow for relative link to local anchor, in TracLinks. Syntax is: `[#anchor optional label]`. In the future, this could be expanded so that any trailing `#...` in the target part of a TracLinks ends up in the href itself. Related to #2168.

Before checking custom validation rules, always Validate ''options'' fields:
- values not in the list of valid values for this option are rejected
- unsetting the field is possible only if the field is declared ''optional''.

Closes #3679.

Follow-up to r3737, the patch renderer should be fully fixed now.

Genshi branch: oops, r3736 was not complete... Also, start the convergence of trac.versioncontrol.diff and trac.mimeviewer.patch common code.

Backported [3736] ''(patch renderer bugfix)''

Markup branch: highlighting of intra-line changes was not triggered for changes at the start or at the end of the line.

Genshi branch: the patch IHTMLPreviewRenderer now reuses the ''diff_div.html'' template.

fix #2256 by providing a workaround for ignoring cookies from other applications with parsing errors

add an option `--single-env` to tracd for serving a single project without the project listing (fixes #3506)

update the milestone name after retargetting tickets to a new milestone (fixes #2743)