gitview: Fix the graph display .

gitview: Fix the graph display .

This fix all the known issue with the graph display
The bug need to be explained graphically

                                 |
                                 a
This line need not be there ---->| \
                                 b  |
                                 | /
                                 c

c is parent of a and all a,b and c are placed on the same line and b is child of c
With my last checkin I added  a seperate line to indicate that a is
connected to c. But then we had the line connecting a and b which should
not be ther. This changes fixes the same bug

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>