Rich Filker spotted that sed -e 's/xxx/[/' didn't work right. Did a smaller

fix than his, and shrank the code a bit on top of that so the net size is
smaller, and added a test to the test suite for this case.  Plus I cleaned up
the #includes and removed unnecessary "const"s while I was there.

testsuite/sed.tests

@@ -174,6 +174,8 @@ testing "sed -i with no arg [GNUFAIL]" "sed -e '' -i 2> /dev/null || echo yes" \
 	"yes\n" "" ""
 rm ./-     # Clean up
 
+testing "sed s/xxx/[/" "sed -e 's/xxx/[/'" "[\n" "" "xxx\n"
+
 # Ponder this a bit more, why "woo not found" from gnu version?
 #testing "sed doesn't substitute in deleted line" \
 #	"sed -e '/ook/d;s/ook//;t woo;a bang;'" "bang" "" "ook\n"