hush: use ash's read builtin

function                                             old     new   delta
shell_builtin_read                                     -    1000   +1000
set_local_var_from_halves                              -      24     +24
setvar2                                                -       7      +7
...
popstring                                            140     134      -6
ash_main                                            1375    1368      -7
setvar                                               184     174     -10
arith_set_local_var                                   36       -     -36
builtin_read                                        1096     185    -911
------------------------------------------------------------------------------
(add/remove: 3/1 grow/shrink: 5/23 up/down: 1038/-1007)        Total: 31 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/hush_test/hush-read/read_n.tests b/shell/hush_test/hush-read/read_n.tests
new file mode 100755
index 0000000..12423ba
--- /dev/null
+++ b/shell/hush_test/hush-read/read_n.tests
@@ -0,0 +1,3 @@
+echo 'test' | (read reply; echo "$reply")
+echo 'test' | (read -n 3 reply; echo "$reply")
+echo 'test' | (read -n3 reply; echo "$reply")