fix other cases of unicode mixing issue

and fix underlaydir override attack guard when srcdir is non-absolute

diff --cc IkiWiki/Render.pm
index 0e7aa9a48a2bd5ddb4267ca948e3f6eba6ba121a,f81e373b73ad37dcdfc988f0f08a08eb2122012d..740bb52b0fc6d9ea1797a08080a273f5fb3701f6
--- 1/IkiWiki/Render.pm
--- 2/IkiWiki/Render.pm
+++ b/IkiWiki/Render.pm
@@@ -295,8 -300,9 +300,8 @@@ sub find_src_files () 
        my ($page, $underlay);
        my $helper=sub {
                my $file=decode_utf8($_);
 -
                return if -l $file || -d _;
-               $file=~s/^\Q.\/\E//;
+               $file=~s/^\.\///;
                return if ! length $file;
                $page = pagename($file);
                if (! exists $pagesources{$page} &&