fix cpan links

doc/bugs/htmlscrubber_undoes_email_obfuscation_by_Text::Markdown.mdwn

@@ -33,5 +33,5 @@ The relevant commits are on the master branch of [my "fork" of ikiwiki on Github
 > `Text::Markdown::_EncodeEmailAddress` gets into its internals more than
 > I'm comfortable with.
 > 
-> It would probably be best to add an option to [[cpan Text;:Markdown]] to
+> It would probably be best to add an option to [[!cpan Text::Markdown]] to
 > let the email address munging be disabled. --[[Joey]]

doc/bugs/ssl_certificates_not_checked_with_openid.mdwn

@@ -40,7 +40,7 @@ For now, I want to try and resolve the issues with net\_ssl\_test, and run more
 >> -- Brian May
 
 >>> I guess that the place to add SSL cert checking would be in either
->>> [[cpan LWPx::ParanoidAgent]] or [[cpan Net::OpenID::Consumer]]. Adding
+>>> [[!cpan LWPx::ParanoidAgent]] or [[!cpan Net::OpenID::Consumer]]. Adding
 >>> it to ikiwiki itself, which is just a user of those libraries, doesn't
 >>> seem right.
 >>> 

doc/todo/structured_page_data.mdwn

@@ -45,10 +45,10 @@ This seems conceptually straightforward, if possibly quite internally
 complex to handle the more complicated types and validation.
 
 One implementation wrinkle is how to build the html form. The editpage.tmpl
-currently overrides the standard [[cpan CGI::FormBuilder]] generated form,
+currently overrides the standard [[!cpan CGI::FormBuilder]] generated form,
 which was done to make the edit page be laid out in a nice way. This,
 however, means that new fields cannot be easily added to it using
-[[cpan CGI::FormBuilder]]. The attachment plugin uses the hack of bouilding
+[[!cpan CGI::FormBuilder]]. The attachment plugin uses the hack of bouilding
 up html by hand and dumping it into the form via a template variable. 
 
 It would be nice if the type implementation code could just use