annotate: do not poorly split lines at CR (issue5798)
mdiff and lines(text) take only LF as a line separator, but str.splitlines()
breaks our assumption. Use mdiff.splitnewlines() consistently.
It's hard to read \r in tests, so \r is replaced with [CR]. I had to wrap
sed by a shell function to silence check-code warning.
#require docutils gettext
$ $TESTDIR/check-gendoc el
checking for parse errors