tigefa4u projects Trac

Strip leading and trailing whitespace from the names of milestones, versions, components, etc. I.e. and ticket field values that get used in a `<select>` control. Fixes #1344.

Homogenize the display of columns in the Browser and Log Revision views

DatabaseBackend refactoring: the old db.py file has been split in several files
now placed in the trac/db subfolder.

Also, a new `IDatabaseBackend` interface has been defined,
and this is used for better dispatching from the database connection string
to the appropriate backend.

This greater flexibility would allow to use the pysqlite1 binding
for one environment and the pysqlite2 binding for another, for example.

While the changes were primarily done for cleaning up the current implementation,
this will also make it easier to add new database backends.

Created a branch for cleaning-up the code related to the DatabaseBackend

TracDiff: r2309 was incomplete, adding the remaining `s/get_deltas/get_changes/`

TracCrossReferences: homogeneize the display of cross-reference contexts

TracCrossReferences: merged changes from trunk (log:trunk@...:2366)

TracCrossReferences: removed the TracDiff and InterTrac features from that branch

Now, this only contains the xref stuff (that is, plenty enough changes :) )
on top of the source:trunk@...

TracCrossReferences: started the implementation of the <<...>> wiki syntax for creating arbitrary relations between !TracObjects

i.e. if in Ticket !#2, one writes: `<<duplicate-of #1>>`, then a `duplicate-of` relationship is created,
with ticket !#2 being the source and ticket !#1 being the target.

Moved the flexible WikiPageNames scheme from InterTrac to FlexibleWikiPageNames, and updated it to the newest way of enabling/disabling plugins