cgi: precheck multiple Ausweichroute records
cgi: enabled file cache also for output_as=json*

It seems that 20% of all JSON requests were repeated (logs from June
2013).
test json file caching
data/Makefile: workaround for older pmake

Old pmake (e.g. in debian/squeeze) does not support the :U modifier.
Rewrote the rule to use echo ... | tr ... instead.
cgi: fixed @custom vs. @current_temp_blocking confusion

@custom is for currently activated temp blockings.
@current_temp_blocking holds all temp blockings valid for the current
time.

The user visible change is that now in case of a not-found route the
text "Keine Route gefunden" is shown instead of the incorrect "Es
existiert keine Ausweichroute".
* data update
server-check.t checks now only localhost

But there's the new -url option to check other URLs. This is currently
used by bbbike-aux/t/server-check.t to test the real server.