tigefa4u projects Trac

Backported some enhancements from the InterTrac wiki formatter to the trunk:
* r1921: support for relative links (closes #691)
* use `cStringIO` instead of `StringIO` if available
* add title optional parameter to `_make_ext_link`

Removed temporary comment that went into r2157

InterTrac: merged with TracDiff (log:branches/cboos-dev/anydiff-branch#2095:2148)

Expand tabs to spaces before rendering HTML previews to ensure that Trac's tabwidth is used. IHTMLPreviewRenderer implementations for text content should define the property `expand_tabs = True` to have Trac expand tabs.

parent_pool should default to application_pool.

Fixed inconsistent indentation and removed some unused code.

Use a new and improved apr pool class by David James. Limit the log view to 100 entries.

Make sure the changeset entries are sorted by path

Use apr subpools to limit memory usage during path_history queries.

Followup to [2149]: make sure that `req.hdf` is cleared by moving the statement before `req.session.save()`.