ci: Update Travis-CI to use Ubuntu Linux 14.04 (trusty) and OS X 10.9 VMs

Due to resource constraints, this commit also makes Travis-CI to build
only once (debug, without precompiled headers, with tests).

Change-Id: I65ec64bca545093efae384dd00b51bbeaf7d9b65
Refs: #3360
diff --git a/wscript b/wscript
index f833255..f51f65a 100644
--- a/wscript
+++ b/wscript
@@ -117,6 +117,9 @@
                    " (http://redmine.named-data.net/projects/nfd/wiki/Boost_FAQ)")
         return
 
+    if conf.env['CXX_NAME'] == 'clang' and conf.env.BOOST_VERSION_NUMBER < 105800:
+        conf.define('BOOST_ASIO_HAS_STD_ARRAY', 1) # Workaround for http://redmine.named-data.net/issues/3360#note-14
+
     conf.load('unix-socket')
     conf.checkWebsocket(mandatory=True)