If even HOME is missing look up the user's home directory from passwd

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Add src/redshift to .gitignore

Signed-off-by: Mattias Andrée <maandree@operamail.com>
When looking for a redshift.conf file do not just check environment variable, also check that the file exists

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Look for configuration file in XDG_CONFIG_DIRS and /etc

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Also look for {~,$HOME}/.redshift.conf

Signed-off-by: Mattias Andrée <maandree@operamail.com>