Check that find_stowed_path $path matches relative/absolute with target

Watch out for a corner case probably only relevant in tests.

lib/Stow.pm.in

@@ -961,6 +961,12 @@ sub find_stowed_path {
     # If no .stow file was found, we need to find out whether it's
     # owned by the current stow directory, in which case $path will be
     # a prefix of $self->{stow_path}.
+    if (substr($path, 0, 1) eq '/' xor substr($self->{stow_path}, 0, 1) eq '/')
+    {
+        warn "BUG in find_stowed_path? Absolute/relative mismatch between " .
+             "Stow dir $self->{stow_path} and path $path";
+    }
+
     my @stow_path = split m{/+}, $self->{stow_path};
 
     # Strip off common prefixes until one is empty