makes the test logs way more readable
Believe me: no one will ever notice a "TODO"
entry in the logs, when it showed up for
more than some months.
Thus I've created some new tickets, mostly
tagged as "QA" and placed the ticket number
at the corresponding locations in the source
lumiera_error_set() now takes an optional extra string which can be used
to pass context relevant data along. This string gets copied into the
error state so one can easily create it by the tmpbuf_snprintf() facility.
Also a lot of places which define errors get fixed according to this.
