for extended pagespecs. The old calling convention will still work for
back-compat for now.
* The calling convention for functions in the IkiWiki::PageSpec namespace
has changed so they are passed named parameters.
* Plugin interface version increased to 2.00 since I don't anticipate any
more interface changes before 2.0.
commit hook, it was possible for one CGI to race another one and "win"
the commit of both their files. This race has been fixed by adding a new
commitlock, which when locked by the CGI, disables the commit hook
(except for commit mails). The CGI then takes care of the updates the
commit hook would have done.