This [[patch]] allows for `\[[sha1]]` substitution in the `diffurl`
for git repositories.  This is useful for use with [cgit][] which has
diffurls of the following form:

    /project.git/diff/\[[file]]?id=\[[sha1]]

 [cgit]: http://hjemli.net/git/cgit/

    diff --git a/IkiWiki/Plugin/git.pm b/IkiWiki/Plugin/git.pm
    index 5bef928..164210d 100644
    --- a/IkiWiki/Plugin/git.pm
    +++ b/IkiWiki/Plugin/git.pm
    @@ -518,6 +518,7 @@ sub rcs_recentchanges ($) { #{{{
     
     			my $diffurl = defined $config{'diffurl'} ? $config{'diffurl'} : "";
     			$diffurl =~ s/\[\[file\]\]/$file/go;
    +			$diffurl =~ s/\[\[sha1\]\]/$sha1/go;
     			$diffurl =~ s/\[\[sha1_parent\]\]/$ci->{'parent'}/go;
     			$diffurl =~ s/\[\[sha1_from\]\]/$detail->{'sha1_from'}/go;
     			$diffurl =~ s/\[\[sha1_to\]\]/$detail->{'sha1_to'}/go;