amp switchrate to avoid Dtrace buffer filling up with 'bunyan -p ...'

CHANGES.md

@@ -8,7 +8,17 @@ Known issues:
 
 ## bunyan 0.21.2 (not yet released)
 
-(nothing yet)
+- Avoid Dtrace buffer filling up, e.g. like this:
+
+        $ bunyan -p 42241 > /tmp/all.log
+        dtrace: error on enabled probe ID 3 (ID 75795: bunyan42241:mod-87ea640:log-trace:log-trace): out of scratch space in action #1 at DIF offset 12
+        dtrace: error on enabled probe ID 3 (ID 75795: bunyan42241:mod-87ea640:log-trace:log-trace): out of scratch space in action #1 at DIF offset 12
+        dtrace: 138 drops on CPU 4
+        ...
+
+  From Bryan: "the DTrace buffer is filling up because the string size is so
+  large... by increasing the switchrate, you're increasing the rate at
+  which that buffer is emptied."
 
 
 ## bunyan 0.21.1

bin/bunyan

@@ -1105,6 +1105,7 @@ function processPids(opts, stylize, callback) {
             return format('bunyan%s:::log-*', pid);
         }).join(',');
         var argv = ['dtrace', '-Z', '-x', 'strsize=4k', '-qn',
+            '-x', 'switchrate=10hz',
             format('%s{printf("%s", copyinstr(arg0))}', probes)];
         //console.log('dtrace argv: %s', argv);
         var dtrace = spawn(argv[0], argv.slice(1),