This changes the on disk format for new raw reports to be gzip
compressed. Also adds the ability to serve these reports in plain text,
to insulate web browsers from the change (previously we just served the
raw reports from disk using Caddy).
Use a global raven.Client because they allocate an http.Client for each,
with a separate CA bundle and infinite connection idle time. Infinite
connection idle time means that if the client is never used again it
will always keep the connection around, not verifying whether it's
closed server side or not. This leaks about a megabyte of memory for
each client every created.
client.Close() doesn't help with this because the http.Client is still
around, retained by its own goroutines.
The thing with the map is just to retain the API on sendReport, even
though there will in practice only ever be one DSN per process
instance...
* lib/ur: Implement crash (panic) reporting (fixes#959)
This implements a simple crash reporting method. It piggybacks on the
panic log files created by the monitor process, picking these up and
uploading them from the usage reporting routine.
A new config value points to the crash receiver base URL, which defaults
to "https://crash.syncthing.net/newcrash" (following the pattern of
"https://data.syncthing.net/newdata" for usage reports, but allowing us
to separate the service as required).
