Update vertx-core/src/main/java/org/vertx/java/core/http/impl/DefaultHttpServerResponse.java

fix multiple Set-Cookie headers issue
Update vertx-core/src/main/java/org/vertx/java/core/http/impl/DefaultHttpServerResponse.java

avoid multiple getValue() invoke (base on previous modification)
UGLY: return multiple Set-Cookie headers
add testMultipleSetCookieHeaders
allow multiple headers with same name in trailer
move test code from JavaHttpTest to HttpTestClient
make cookies() abstract
Merge branch 'master' of https://github.com/figroc/vert.x into test_merge6