Don't use "git log -p" in the test suite.

The exact format of "git log -p" may change due to user configuration,
and even if the test suite can try to set all configuration that
influences the format explicitly it is hard to guard against future
changes in git.  Since we already run "cmd list_files" immediately
before all instances of running "git log -p", we are still assured
that the history contains what we expect.

There was one instance in t-021.sh where "cmd git log -p" were not
preceded by "cmd list_files".

Signed-off-by: Per Cederqvist <[email protected]>
Signed-off-by: Josef 'Jeff' Sipek <[email protected]>