Won't compile on AppEngine

[rcrowley]

Per rcrowley/go-tigertonic#75, go-metrics won't compile on App Engine because it uses runtime.NumCgoCall, among probably other verboten variables.

[rcrowley]

@pshevtsov, can you please verify whether this fixes the build issue on AppEngine?

[przmv]

@rcrowley unfortunately the changes do not fix the build issue:

05:09 PM Error 422: --- begin server output ---
Compile failed:
2014/08/06 06:09:38 go-app-builder: build timing: 5×6g (668ms total), 8×gopack (284ms total), 0×6l (0 total)
2014/08/06 06:09:38 go-app-builder: failed running 6g: exit status 1

github.com/rcrowley/go-metrics/runtime.go:128: undefined: numCgoCall
--- end server output ---

Probably it would be better to use !appengine and appengine build constraints as it was described here http://blog.golang.org/the-app-engine-sdk-and-workspaces-gopath .

[mihasya]

This appears to be fixed by an already merged PR! More issues like this please!