build: revert AM_TESTS_ENVIRONMENT to TESTS_ENVIRONMENT

* Makefile.am: prefer TESTS_ENVIRONMENT rather than AM_TESTS_ENVIRONMENT
  to avoid problems with older automake versions.  For example Travis-CI
  is not working because of this issue, or Debian stable cannot be used
  to build upstream GNU Hello.
* configure.ac: automake 1.12 or newer will not allow combination of
  parallel-tests and TESTS_ENVIRONMENT.

Reference:
http://lists.gnu.org/archive/html/bug-hello/2014-07/msg00003.html

diff --git a/Makefile.am b/Makefile.am
line changes: +1/-1
index 352898b..73c0b39
--- a/Makefile.am
+++ b/Makefile.am

@@ -75,7 +75,7 @@ BUILT_SOURCES =
 
 LOG_COMPILER = $(SHELL)
 
-AM_TESTS_ENVIRONMENT = \
+TESTS_ENVIRONMENT = \
   top_srcdir=$(top_srcdir) \
   PATH=.$(PATH_SEPARATOR)$(PATH_SEPARATOR)$$PATH \
   HELLO=`echo hello | sed '$(transform)'`; \

diff --git a/configure.ac b/configure.ac
line changes: +0/-1
index 2ac1fa2..30a9d0c
--- a/configure.ac
+++ b/configure.ac

@@ -18,7 +18,6 @@ AC_CONFIG_AUX_DIR([build-aux])
 AM_INIT_AUTOMAKE([
 	1.11.1
 	readme-alpha
-	parallel-tests
 	subdir-objects
 ])