Add sed(1) tests for proper behaviour of the G option as fixed in PR 26152,

and for proper behaviour of some sed functions given a nil pattern space,
as fixed in PR 34813.

The test for G was based on the test in the PR.  The nil pattern space test
is slightly different as we need to get *some* output, as the core dump will
also produce no output (old behaviour) and turn up falsely that the utility
is working fine.

tools/regression/usr.bin/Makefile

@@ -1,5 +1,5 @@
 # $FreeBSD$
 
-SUBDIR=	file2c join jot make uudecode uuencode xargs
+SUBDIR=	file2c join jot make sed uudecode uuencode xargs
 
 .include <bsd.subdir.mk>

tools/regression/usr.bin/sed/Makefile

@@ -0,0 +1,4 @@
+# $FreeBSD$
+
+all:
+	@sh ${.CURDIR}/regress.sh ${.CURDIR}

tools/regression/usr.bin/sed/regress.G.out

@@ -0,0 +1,8 @@
+input
+
+data
+
+for validation
+
+of sed(1)
+

tools/regression/usr.bin/sed/regress.in

@@ -0,0 +1,4 @@
+input
+data
+for validation
+of sed(1)

tools/regression/usr.bin/sed/regress.psl.out

@@ -0,0 +1 @@
+of sed(1)

tools/regression/usr.bin/sed/regress.sh

@@ -0,0 +1,30 @@
+# $FreeBSD$
+
+# Go into the regression test directory, handed to us by make(1)
+TESTDIR=$1
+if [ -z "$TESTDIR" ]; then
+  TESTDIR=.
+fi
+cd $TESTDIR
+
+STATUS=0
+
+for test in G psl; do
+  echo "Running test $test"
+  case "$test" in
+  G)
+    sed G < regress.in | diff -u regress.$test.out -
+    ;;
+  psl)	
+    sed '$!g; P; D' < regress.in | diff -u regress.$test.out -
+    ;;
+  esac
+  if [ $? -eq 0 ]; then
+    echo "Test $test detected no regression, output matches."
+  else
+    STATUS=$?
+    echo "Test $test failed: regression detected.  See above."
+  fi
+done
+
+exit $STATUS