TigOpenFileWithCommit is broken

[maxigit]

:TigOpenFileWithCommit without arguments used to call tig_explorer#open_file_with_commit with no arguments using the default value being the current file and head.

:TigOpenFileWithCommit! would then open a diff with the current head version. Handy to see what has changed. This doesn't work anymore since tig_explorer#open_file_with_commit has been changed to only accept a fixed number of argument (I'm not sure why).
Now you have to type explicitely :TigOpenFileWithCommit HEAD % 0.