New plugin: loop (#1989)

* New plugin: loop

Add a plugin that detects loops. It does this by sending an unique query
to our selves. If we see the query more than twice we stop the process.
If there isn't a loop, the plugin disables it self and becomes a noop
plugin.

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/pkg/log/plugin.go

@@ -3,6 +3,7 @@ package log
 import (
 	"fmt"
 	golog "log"
+	"os"
 )
 
 // P is a logger that includes the plugin doing the logging.
@@ -58,4 +59,10 @@ func (p P) Error(v ...interface{}) { p.log(err, v...) }
 // Errorf logs as log.Errorf.
 func (p P) Errorf(format string, v ...interface{}) { p.logf(err, format, v...) }
 
+// Fatal logs as log.Fatal and calls os.Exit(1).
+func (p P) Fatal(v ...interface{}) { p.log(fatal, v...); os.Exit(1) }
+
+// Fatalf logs as log.Fatalf and calls os.Exit(1).
+func (p P) Fatalf(format string, v ...interface{}) { p.logf(fatal, format, v...); os.Exit(1) }
+
 func pFormat(s string) string { return "plugin/" + s + ": " }