git-gui: Run blame twice on the same file and display both outputs
We now perform two passes over any input file given to the blame viewer. Our first pass is a quick "git-blame" with no options, getting the details of how each line arrived into this file. We are specifically ignoring/omitting the rename detection logic as this first pass is to determine why things got into the state they are in.
Once the first pass is complete and is displayed in the UI we run a second pass, using the much more CPU intensive "-M -C -C" options to perform extensive rename/movement detection. The output of this second pass is shown in a different column, allowing the user to see for any given line how it got to be, and if it came from somewhere else, where that is.
This is actually very instructive when run on our own lib/branch.tcl script. That file grew recently out of a very large block of code in git-gui.sh. The first pass shows when I created that file, while the second pass shows the original commit information.
Signed-off-by: Shawn O. Pearce <email@example.com>