Add new argument $basepage to WikiPlugin::run() and WikiPluginLoader::expandPI().

Add new argument $basepage to WikiPlugin::run() and WikiPluginLoader::expandPI().
Plugins need to know what page they were invoked from so that they can handle
relative page links (like [/Subpage]) correctly.  ($request->getArg('pagename')
is not always the right page to use --- think included pages...)

Many plugins don't need the $basepage, in which case, I think they can just ignore
the extra argument.  (I don't think PHP will generate any warnings.)

Also: deleted <?plugin-head?> code.  It's not needed any more, now that
we always cache output.

The FrameInclude plugin seems broken now, though I'm not convinced it's
my fault.  If it is, sorry...   (I'll try to look at it a bit more
within a few days, to see if I can figure out the problem.)

git-svn-id: svn://svn.code.sf.net/p/phpwiki/code/trunk@2632 96ab9672-09ca-45d6-a79d-3d69d39ca109