Merge branch 'http-client-fix-expect-100-continue-v6'

This patch set fixes and covers http client and "Expect: 100-continue"
functionality (plus increase coverage under some related options, to avoid
further regressions).

* http-client-fix-expect-100-continue-v6:
  http: fix leaking of response_code_line
  http: fix "Expect: 100-continue" client side
  test/http: separate coverage for EVHTTP_CON_READ_ON_WRITE_ERROR
  test/http: cover "Expect: 100-continue" client-server interaction
  test/http: *lingering tests shouldn't have "Expect: 100-continue"