Reported by Matthew Dawson, May 1, 2010

Currently, there is no way to specify the text that is used when a 
link is created to a documentation page.  Links look like: 
[[WikiPage]].  With this patch a new format is accepted: [My Link 
Text]([[WikiPage]]).  This allows for old style links to keep 
working and allows for quick updates to the new syntax.  The new 
format is similar to what markdown text looks like too.

It also fixes up what to display when users don't have access to 
documentation, as the previous behaviour was confusing to me.  The 
new behaviour should be more consistent and easy to understand.  
When the documentation is disabled, it simply passes through the 
link.  Otherwise, if the user has no access it ignores the link part 
and just displays the link text.  If the user does have access, then 
the link is created in the usual form (if the page does not exist, 
make a link to create it, otherwise make a link to the page).