WIP faster denodeify

note quite feature parity, but will work to restore at least some of it.

```
node performance.js ./doxbee-sequential/*.js  --n 10000 --t 1 --p 50  --harmony
results for 10000 parallel executions, 1 ms per I/O op

file                                 time(ms)  memory(MB)
promises-tildeio-rsvp.js                  732       86.87
promises-tildeio-rsvp.js                 1414      153.18 (before)


node performance.js ./doxbee-sequential-errors/*.js  --n 10000 --t 1 --p 50  --harmony
results for 10000 parallel executions, 1 ms per I/O op

file                                 time(ms)  memory(MB)
promises-tildeio-rsvp.js                  910       86.65
promises-tildeio-rsvp.js                 1159      136.48 (before)


node performance.js ./madeup-parallel/*  --n 10000 --t 1 --p 50  --harmony
results for 10000 parallel executions, 1 ms per I/O op

file                                time(ms)  memory(MB)
promises-tildeio-rsvp.js                2503      361.20
promises-tildeio-rsvp.js               17998     1280.76 (before)
```

platform:
```
Platform info:
Darwin 13.2.0 x64
Node.JS 0.11.11
V8 3.22.24.19
Intel(R) Core(TM) i7-4650U CPU @ 1.70GHz × 4
```

full suite runs: https://gist.github.com/stefanpenner/ddcf229992443acee362