Add global replace for processing raw headers

[kwgithubusername]

@mislav @mpfluger

Added global replace as @pseidemann mentioned.
#491 (comment)

Not sure how you would want to expose parseHeaders for testing but here are some suggestions for tests:

suite('parseHeaders', function() {
  test('parses raw headers with line feed'), function() {
    var rawHeaders = 'Tolerance-Provision-Value-1: key1\nTolerance-Provision-Value-2: key2\nTolerance-Provision-Value-3: key3'
    var headers = parseHeaders(rawHeaders);
    assert.equal(headers.get('Tolerance-Provision-Value-1'),'key1')
    assert.equal(headers.get('Tolerance-Provision-Value-2'),'key2')
    assert.equal(headers.get('Tolerance-Provision-Value-3'),'key3')
  })
  test('parses raw headers with carriage return line feed'), function() {
    var rawHeaders = 'Basic-Rules-Value-1: key1\r\nBasic-Rules-Value-2: key2\r\nBasic-Rules-Value-3: key3'
    var headers = parseHeaders(rawHeaders);
    assert.equal(headers.get('Basic-Rules-Value-1'),'key1')
    assert.equal(headers.get('Basic-Rules-Value-2'),'key2')
    assert.equal(headers.get('Basic-Rules-Value-3'),'key3')
  })
  test('parses raw headers with obs-fold'), function() {
    var rawHeaders = 'Obs-Fold-Value: key1\r\n key2\r\n key3'
    var headers = parseHeaders(rawHeaders);
    assert.equal(headers.get('Obs-Fold-Value'),'key1 key2 key3')
  })
})

[mislav]

Thanks for the fix! Unfortunately, it's not easy to test this with our current setup, so let's get this in without tests. If only Node let us supply our own response headers in raw format, then it would be easier to test this.