travis: retry test deps setup as their dl regularly fail

Add a 'test-deps' make target to specifically build all dependencies for
tests, like Nagelfar and Tcl8.3 download. Call this specific target in
Travis CI through the `travis_retry` utility to retry dependency
download if they fail.

Author: xdelaruelle

.travis.yml

@@ -337,6 +337,7 @@ script:
   - $CMD_PREFIX ./configure $CONFIGURE_OPTS
   - $CMD_PREFIX make
   - if [ -n "$EXTRA_SCRIPT_PRETEST" ]; then $CMD_PREFIX eval $EXTRA_SCRIPT_PRETEST; fi
+  - travis_retry $CMD_PREFIX make test-deps
   - travis_wait 25 unbuffer $CMD_PREFIX script/mt
   - if [ -n "$EXTRA_SCRIPT_POSTTEST" ]; then $CMD_PREFIX eval $EXTRA_SCRIPT_POSTTEST; fi
   - $CMD_PREFIX make install

Makefile

@@ -2,8 +2,8 @@
 	install-testsiteconfig-1 install-testmodulerc install-testmodulerc-1 \
 	install-testinitrc install-testetcrc install-testmodspath \
 	install-testmodspath-empty uninstall-testconfig uninstall dist dist-tar \
-	dist-gzip dist-bzip2 dist-win srpm rpm clean distclean test testinstall \
-	testsyntax
+	dist-gzip dist-bzip2 dist-win srpm rpm clean distclean test-deps test \
+	testinstall testsyntax
 
 # download command and its options
 WGET := wget --timeout=5 --tries=2
@@ -639,6 +639,9 @@ ifeq ($(COVERAGE),y)
 export MODULECMD = $(MODULECMDTEST)_i
 endif
 
+# specific target to build test dependencies
+test-deps: $(TEST_PREREQ)
+
 # if coverage enabled create markup file for better read coverage result
 test: $(TEST_PREREQ)
 ifeq ($(compatversion) $(wildcard $(COMPAT_DIR)),y $(COMPAT_DIR))