Semantic errors (for example, for alias.* variables NULL values are
not allowed) in configuration files cause a die printing the line
number and file name of the offending value.
Add a test documenting that such errors cause a die printing the
accurate line number and file name.
Signed-off-by: Tanay Abhra <tanayabh@gmail.com> Reviewed-by: Matthieu Moy <Matthieu.Moy@imag.fr> Signed-off-by: Junio C Hamano <gitster@pobox.com>