This teaches "git bisect visualize" to be more useful in non-windowed
environments.

 (1) When no option is given, and $DISPLAY is set, it continues to
     spawn gitk as before;

 (2) When no option is given, and $DISPLAY is unset, "git log" is run
     to show the range of commits between the bad one and the good ones;

 (3) If only "-flag" options are given, "git log <options>" is run.
     E.g. "git bisect visualize --stat"

 (4) Otherwise, all of the given options are taken as the initial part
     of the command line and the commit range expression is given to
     that command.  E.g. "git bisect visualize tig" will run "tig"
     history viewer to show between the bad one and the good ones.

As "visualize" is a bit too long to type, we also give it a shorter
synonym "view".

Signed-off-by: Junio C Hamano <gitster@pobox.com>