Support for InterWiki links

An InterWiki link can be used for referring to a Wiki page located in another Wiki system, and by extension, to any object located in any other Web application, provided a simple URL mapping can be done.

InterWiki prefixes can even be used to simply introduce links to new protocols, such as `tsvn:` used by TortoiseSvn.

<target_wiki>(:<identifier>)+

The link is composed by the targeted Wiki (or system) name, followed by a colon, eg `MeatBall:`, followed by a page specification in the target. Note that, as for InterTrac prefixes, InterWiki prefixes are case insensitive.

The target Wiki URL is looked up in the `interwiki` section of TracIni or in the InterMapTxt wiki page, modeled after MeatBall:InterMapTxt. If a prefix is defined in both the `interwiki` section and InterMapTxt, the `interwiki` section takes precedence.

In addition to traditional InterWiki links, where the target is simply appended to the URL, Trac supports parametric InterWiki URLs: identifiers `$1`, `$2`, … in the URL will be replaced by corresponding arguments. The argument list is formed by splitting the page identifier using the “:” separator.

Every option in the `interwiki` section in TracIni defines one InterWiki prefix. The option name defines the prefix. The option value defines the URL, optionally followed by a description separated from the URL by whitespace. Parametric URLs are supported as well.

Example:

#!ini
[[:interwiki]]
MeatBall = http://www.usemod.com/cgi-bin/mb.pl?
PEP = http://www.python.org/peps/pep-$1.html Python Enhancement Proposal $1
tsvn = tsvn: Interact with TortoiseSvn

If the following is an excerpt of the InterMapTxt page:

====== InterMapTxt ======
===== This is the place for defining InterWiki prefixes =====

Currently active prefixes: [[:[InterWiki]]]

This page is modelled after the MeatBall:InterMapTxt page.
In addition, an optional comment is allowed after the mapping.
----
<code>
PEP      http://www.python.org/peps/pep-$1.html           # Python Enhancement Proposal $1 
Trac-ML  http://thread.gmane.org/gmane.comp.version-control.subversion.trac.general/$1  # Message $1 in Trac Mailing List

tsvn     tsvn:                                            # Interact with TortoiseSvn
...
MeatBall http://www.usemod.com/cgi-bin/mb.pl?
MetaWiki http://sunir.org/apps/meta.pl?
MetaWikiPedia http://meta.wikipedia.org/wiki/
MoinMoin http://moinmoin.wikiwikiweb.de/
...

</code>

Then,

• `MoinMoin:InterWikiMap` should be rendered as MoinMoin:InterWikiMap and the title for that link would be “!InterWikiMap in MoinMoin”.
• `Trac-ML:4346` should be rendered as Trac-ML:4346 and the title for that link would be “Message 4346 in Trac Mailing List”.

See also: InterTrac, InterMapTxt