Problem: cppzmq build broken with C++11 compiler and git cloned repo.

Default build, ./ci_build.sh without any arguments, which causes to run
with draft disabled, does not work properly for git cloned repository and
C++11 compiler.

Two issues:
1. For git cloned repository ENABLE_DRAFTS is ON by default but libzmq
compiled build without drafts .Travis did not catch that because default build
runs on non C++11 compiler.
2. testutil.hpp does not build because of missing draft guards.

Solution 1: Remove check for presence of .git for enabling draft API as it
is confusing to use with ENABLE_DRAFTS flag and there should be only one
explicit way to enable draft build.

Solution 2: add missing draft guards in testutil.hpp for server/client
socket in use there.

Solution 3: add extra Travis build covering C++11 compiler and non
draft enabled build.

tests/testutil.hpp

@@ -3,7 +3,7 @@
 #include <gtest/gtest.h>
 #include <zmq.hpp>
 
-#if defined(ZMQ_CPP11)
+#if defined(ZMQ_BUILD_DRAFT_API) && defined(ZMQ_CPP11)
 #include <array>
 
 class loopback_ip4_binder