This reverts commit a2f70da4.

Keep tests modifies a few edge checks on Copy()

thanks to ES5 features in V8 it is quite easily possible.

Automatically set Options.options.jobs to the number of CPUs/cores on the
executing machine, unless the environment variable JOBS is set

Improve test-buffer.js to cover all copy error cases.

Fix off by one error in string_decoder.

and there was much rejoicing

Thanks to Peter Griess <pg@std.in> for the bug report.

Darwin, Linux, Solaris. FreeBSD still needs testing.

TODO: Amend the tests where we use spawn with argv[0].

- Concatenate 'accept', 'accept-charset', 'accept-encoding',
  'accept-language', 'connection', 'cookie', and 'x-*' headers.
- For all others, drop duplicates.