Fix find_basedir() and display_help()

Fixes two regressions introduced in 21fc7a4 (Replace several uses of
snprintf() by asprintf(), 2014-07-21).

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>
Do not error out when calling xfree(NULL)

Calling free() with NULL as parameter is perfectly safe, no need to
error out here.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>
ui-day.c: Reorganize some free() operations

Fixes regressions introduced in 21fc7a4 (Replace several uses of
snprintf() by asprintf(), 2014-07-21).

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>