change default strftime format for better portability
On some systems, such as Solaris and HP-UX, "%c" format
give output without the leading zero on the single-digit
month-day.
%% should show b unknown
? b
%% should show b unknown and c modified
M c
? b
%% should show b added and c modified
M c
A b
%% should show a removed, b added and c modified
M c
A b
R a
%% should show b added and c modified
M c
A b
%% should show b unknown and c modified
M c
? b
%% should show b unknown
? b
%% should show a b and c
a
b
c