Import data from stdin when the import file is "-"
Import data from stdin when the import file is "-"

Support "-" as file name to the -i/--import option and read from stdin
when that file is specified.

Signed-off-by: Lukas Fleischer <c9ca73f8336dcfb037ec2c2abf52d80a6847a5cd@calcurse.org>

lfos/calcurse,lfos/calcurse,lfos/calcurse