Report request errors

[pimterry]

Using the test from @stefan-guggisberg's PR (#28), this implementation adds support for reporting initial connection errors, so that the test passes.

This fixes #27 (at least for the initial connection error case - I'm not 100% sure that all possible errors after the initial connection are correctly handled, but I haven't seen any obvious issues).

Without this change, initial request errors (any connection that fails before identification is complete) crash the node process completely!

The implementation here:

• Adds an emitError function to client requests. It's the same as clientRequest.emit('error'), except it also works if you call it before the initial request is set up (i.e. before take(request) has been called).
• Checks for errors on the initial socket that's created in identifyConnection, and then adds an error parameter to the callback there and in holdConnectionToIdentification to pass any errors back.
• Calls ClientRequest.emitError(error) in handleClientRequest, if the holdConnectionToIdentification call there fails.

[coveralls]

Pull Request Test Coverage Report for Build 93

• 16 of 17 (94.12%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.3%) to 79.524%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
lib/request.js	16	17	94.12%
<!--	Total:	16	17	94.12%	-->

Totals
Change from base Build 83:	0.3%
Covered Lines:	350
Relevant Lines:	408

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💛 - Coveralls