When trying to insert the raw content of an attached shell script
called `whatever` using:

    \[[!inline pages="whatever" raw="yes"]]

The generated HTML contains:

    \[[!inline Erreur: Can't call method "param" on an undefined value
    at /usr/local/share/perl/5.10.0/IkiWiki/Plugin/inline.pm
    line 346.]]

Looking at the inline plugin's code, it is clear that `$template` is
undef in such a situation. Defining `$template` just before line 346,
in case it's not defined, removes the error message, but nothing
gets inlined as `get_inline_content` returns the empty string in
this situation.

If we explicitely don't want to allow raw inlining of unknown page
types, ikiwiki should output a better error message.