gitstats: Bugfix, created a missing test for "diff -n"

gitstats: Bugfix, created a missing test for "diff -n"

Due to the fact that the setupRepo script did not provide
in cases where a commit was reverted, and then another
change was made in a later commit in the same place, but
with different content, it was impossible to create a test
for the "diff -n" option. The setupRepo script was updated
to include such a case, so now this testcase has been
written.

Bug-introduced-in: 12538cf58ccdf72ab708fd2cf665084fcfa6c259