tests: make test runner a script, not a shell function

All the test scripts in the diffutils testsuite are shell scripts,
so the current definition of TESTS_ENVIRONMENT, which adaptively
run tests using either perl or the shell depending on their kind,
is an overkill.

Moreover, this change is required in order for the testsuite to
continue to work with the new testsuite harness that is planned
to be introduced in Automake 1.12 (which, as of the writing date,
is still under development and in late alpha state).

See also related discussion on bug-coreutils:
 <http://debbugs.gnu.org/cgi/bugreport.cgi?bug=8887>

* tests/Makefile.am (TESTS_ENVIRONMENT): Remove definition of the
`shell_or_perl_' shell function, which is not required anymore.
(LOG_COMPILER): New, define to `$(SHELL)'.
* tests/binary: Make executable.
* tests/colliding-file-names: Likewise.
* tests/excess-slash: Likewise.
* tests/no-newline-at-eof: Likewise.

tests/Makefile.am

@@ -22,21 +22,6 @@ TESTS_ENVIRONMENT =				\
   tmp__=$$TMPDIR; test -d "$$tmp__" || tmp__=.;	\
   TMPDIR=$$tmp__; export TMPDIR;		\
   exec 9>&2;					\
-  shell_or_perl_() {				\
-    if grep '^\#!/usr/bin/perl' "$$1" > /dev/null; then			\
-      if $(PERL) -e 'use warnings' > /dev/null 2>&1; then		\
-	grep '^\#!/usr/bin/perl -T' "$$1" > /dev/null && T_=T || T_=;	\
-        $(PERL) -w$$T_ -I$(srcdir) -MCoreutils				\
-	      -M"CuTmpdir qw($$f)" -- "$$1";	\
-      else					\
-	echo 1>&2 "$$tst: configure did not find a usable version of Perl," \
-	  "so skipping this test";		\
-	(exit 77);				\
-      fi;					\
-    else					\
-      $(SHELL) "$$1";				\
-    fi;						\
-  };						\
   export					\
   VERSION='$(VERSION)'				\
   abs_top_builddir='$(abs_top_builddir)'	\
@@ -55,7 +40,9 @@ TESTS_ENVIRONMENT =				\
   PREFERABLY_POSIX_SHELL='$(PREFERABLY_POSIX_SHELL)' \
   REPLACE_GETCWD=$(REPLACE_GETCWD)		\
   PATH='$(abs_top_builddir)/src$(PATH_SEPARATOR)'"$$PATH" \
-  ; shell_or_perl_
+  ;
+
+LOG_COMPILER= $(SHELL)
 
 built_programs =							\
   echo 'spy:;@echo $$(PROGRAMS)'					\