.travis.yml: add VERBOSE=1 to make flags in order to log test failures

"As with the serial harness above, by default one status line is printed
per completed test, and a short summary after the suite has completed.
However, standard output and standard error of the test are redirected
to a per-test log file, so that parallel execution does not produce
intermingled output. The output from failed tests is collected in the
test-suite.log file. If the variable ‘VERBOSE’ is set, this file is
output after the summary."

(http://www.gnu.org/software/automake/manual/html_node/Parallel-Test-Harness.html)

.travis.yml

@@ -9,6 +9,6 @@ install:
 
 script:
     - ./autogen.sh
-    - ./configure && make distcheck && make clean
+    - ./configure && make distcheck VERBOSE=1 && make clean
     - ./configure --enable-valgrind-tests && make distcheck
-      DISTCHECK_CONFIGURE_FLAGS="--enable-valgrind-tests" && make clean
+      DISTCHECK_CONFIGURE_FLAGS="--enable-valgrind-tests" VERBOSE=1 && make clean