When the user clicks on a commit link within one of the columns in the blame viewer we now jump them not just to that commit/file pair but also to the line of the original file. This saves the user a lot of time, as they don't need to search through the new file data for the chunk they were previously looking at.
We also restore the prior view when the user clicks the back button to return to a pior commit/file pair that they were looking at.
Turned out this was quite tricky to get working in Tk. Every time I tried to jump the text widgets to the correct locations by way of the "yview moveto" or "see" subcommands Tk performed the change until the current event finished dispatching, and then reset the views back to 0, making the change never take place. Forcing Tk to run the pending events before we jump the UI resolves the issue.
Signed-off-by: Shawn O. Pearce <firstname.lastname@example.org>