Tmain: provide the way to skip a test case

If a test case exits with code 77, the comparisons
are never done. It is just skipped.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>

Tmain/tmain-skip-example.d/run.sh

@@ -0,0 +1,6 @@
+if ${CTAGS} --list-features | grep -q afasdfasfasfsa; then
+    echo
+else
+    echo "exapmle: no such feature"
+    exit 77
+fi

Tmain/tmain-skip-example.d/stdout-expected.txt

@@ -0,0 +1 @@
+THIS FILE WILL NOT BE USE.

docs/tmain.rst

@@ -37,6 +37,8 @@ In the example, *Tmain* does:
 
 See also `tmain_run` and `tmain_compare` functions in `misc/units`.
 
+If run.sh exits with code 77, the test case is skipped.
+
 
 TODO
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

misc/units

@@ -1630,6 +1630,7 @@ tmain_compare()
     fi
 }
 
+CODE_FOR_IGNORING_THIS_TMAIN_TEST=77
 tmain_run ()
 {
     local topdir=$1
@@ -1643,6 +1644,8 @@ tmain_run ()
     local aspect
     local engine
 
+    local r
+    local a
     local status=0
 
     basedir=$(pwd)
@@ -1661,7 +1664,19 @@ tmain_run ()
 	    cd ${subdir}
 	    ${SHELL} run.sh ${basedir}/${CTAGS} ${basedir}/${DATADIR} ${basedir}/${LIBEXECDIR}
 	) > ${subdir}/stdout-actual.txt 2> ${subdir}/stderr-actual.txt
-	echo $? > ${subdir}/exit-actual.txt
+	r=$?
+	echo $r > ${subdir}/exit-actual.txt
+
+	if [ $r = $CODE_FOR_IGNORING_THIS_TMAIN_TEST ]; then
+	    run_result skip '/dev/null' "$(cat ${subdir}/stdout-actual.txt)"
+	    for a in ${subdir}/*-actual.txt; do
+		if [ -f "$a" ]; then
+		    rm $a
+		fi
+	    done
+	    echo
+	    continue
+	fi
 
 	if [ -f ${subdir}/tags ]; then
 	    mv ${subdir}/tags ${subdir}/tags-actual.txt