virsh: Elide backslash-newline in batch mode

The previous patch made it possible to split multiple commands by
adding newline, but not to split a long single command. The sequence
backslash-newline was being used as if it were a quoted newline
character, rather than completely elided the way the shell does.

Again, add more tests, although this time it seems more like I am
suffering from a leaning-toothpick syndrome with all the \.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>

tests/virshtest.c

@@ -414,6 +414,9 @@ mymain(void)
     /* Tests of multiple commands.  */
     DO_TEST(36, "a\nb\n", " echo a; echo b;");
     DO_TEST(37, "a\nb\n", "\necho a\n echo b\n");
+    DO_TEST(38, "a\nb\n", "ec\\\nho a\n echo \\\n b;");
+    DO_TEST(39, "a\n b\n", "\"ec\\\nho\" a\n echo \"\\\n b\";");
+    DO_TEST(40, "a\n\\\n b\n", "ec\\\nho a\n echo '\\\n b';");
 
 # undef DO_TEST