Testsuite fixes for ksh.

[Ralf Wildenhues]

Pushed a couple of trivial fixes.

Cheers,
Ralf

        Testsuite fixes for ksh.
        * tests/check10.test: Add ':' as last command in subshell, for
        zero exit status of the subshell.
        * tests/parallel-am.test: Do not let failing 'unset' of
        nonexistent variable exit the test.
        * tests/parallel-am2.test: Likewise.
        * tests/parallel-am3.test: Likewise.

diff --git a/tests/check10.test b/tests/check10.test
index c817dcb..138331c 100755
--- a/tests/check10.test
+++ b/tests/check10.test
@@ -72,6 +72,7 @@ unset TESTS || :
   env TESTS="xpass xpass2" $MAKE -e check
   env TESTS='pass skip xfail' $MAKE -e check
   $MAKE check
+  :
 ) >stdout
 cat stdout
 
diff --git a/tests/parallel-am.test b/tests/parallel-am.test
index 8bd5585..e2101e5 100755
--- a/tests/parallel-am.test
+++ b/tests/parallel-am.test
@@ -81,7 +81,7 @@ $ACLOCAL
 # Further, automake output should be stable.
 
 # Generate expected output using the non-threaded code.
-unset AUTOMAKE_JOBS
+unset AUTOMAKE_JOBS || :
 AUTOMAKE_run 0 --add-missing
 mv stderr expected
 Makefile_ins=`find . -name Makefile.in`
diff --git a/tests/parallel-am2.test b/tests/parallel-am2.test
index b92b79e..9e002ba 100755
--- a/tests/parallel-am2.test
+++ b/tests/parallel-am2.test
@@ -61,7 +61,7 @@ $ACLOCAL
 # Thus we install the auxiliary files in a prior step.
 
 # Generate expected output using non-threaded code.
-unset AUTOMAKE_JOBS
+unset AUTOMAKE_JOBS || :
 rm -f install-sh missing depcomp
 AUTOMAKE_fails --add-missing
 mv stderr expected
diff --git a/tests/parallel-am3.test b/tests/parallel-am3.test
index b3b0aac..11e4706 100755
--- a/tests/parallel-am3.test
+++ b/tests/parallel-am3.test
@@ -57,7 +57,7 @@ mkdir build-aux
 $ACLOCAL
 
 # Generate expected output using the non-threaded code.
-unset AUTOMAKE_JOBS
+unset AUTOMAKE_JOBS || :
 AUTOMAKE_run 0 --add-missing
 mv stderr expected
 mv Makefile.in Makefile.in.exp