This is a cherry-pick of the tests from the following commits:

core.autocrlf=true and core.safecrlf=true did not fail on LF-only file as vanilla git does
Adding a CRLF-file with core.autocrlf=input and core.safecrlf=true does not fail as with vanilla git
Make files with #CR!=#CRLF not fail with core.safecrlf=true

Reported-by: Yue Lin Ho <b8732003@student.nsysu.edu.tw>
Signed-off-by: Sven Strickroth <email@cs-ware.de>