Recent versions of Text::Markdown as found on CPAN (e.g. 1.0.16) no longer contains a Text::Markdown::Markdown() routine, but instead contains a Text::Markdown::markdown() routine (notice the difference in capitalization).
It seems that the Text::Markdown module as found on CPAN is now identical to Text::MultiMarkdown - hence the subtle change.
This patch allows IkiWiki to work with either of the two: