Detect ENOENT by code instead of errno
Detect ENOENT by code instead of errno

I believe the errno value has changed between Node.js versions (specifically,
it was not `34` in v0.11.14). Changed this to detect on the error code instead
of the errno, since the actual error is the same across Node versions.

Test suite now passes in 0.10.35 and 0.11.14.

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