git-gui: Cleanup minor nits in blame code

git-gui: Cleanup minor nits in blame code

We can use [list ...] rather than "", especially when we are talking
about values as then they are properly escaped if necessary.  Small
nit, but probably not a huge deal as the only data being inlined here
is Tk paths.

Some of the lines in the parser code were longer than 80 characters
wide, and they actually were all the same value on the end part of
the line.  Rather than keeping the mess copied-and-pasted around we
can set the last argument into a local variable and reuse it many
times.

The commit display code was also rather difficult to read on an 80
character wide terminal, so I'm moving it all into a double quoted
string that is easier to read.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>