hush: implement $LINENO bashism

function                                             old     new   delta
run_pipe                                            1697    1774     +77
unset_local_var_len                                  258     301     +43
hush_main                                           1009    1051     +42
set_local_var                                        516     554     +38
parse_and_run_file                                    42      75     +33
i_getch                                               96     116     +20
.rodata                                            18858   18876     +18
done_command                                         106     122     +16
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 8/0 up/down: 287/0)             Total: 287 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/hush_test/hush-vars/var_LINENO1.right b/shell/hush_test/hush-vars/var_LINENO1.right
new file mode 100644
index 0000000..31e1a44
--- /dev/null
+++ b/shell/hush_test/hush-vars/var_LINENO1.right
@@ -0,0 +1,8 @@
+2:2
+3:3
+4:4
+5:5
+2:2
+3:3
+4:4
+5:5