check_tcp: fix help description regarding escape option

The help description should print '\\' for backslash not just '\'.

Signed-off-by: Sebastian Herbszt <herbszt@gmx.de>
NEWS: Updating all the fixes
THANKS.in: Add new authors
Prepare release
NEWS: Modify list of changes for 2.1.1 release

Make the list of changes slightly more descriptive.