hush: add support for "set -e"

function                                             old     new   delta
run_list                                             978    1046     +68
o_opt_strings                                         24      32      +8
reset_traps_to_defaults                              136     142      +6
pick_sighandler                                       57      60      +3
packed_usage                                       31772   31770      -2
hush_main                                            983     961     -22
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 4/2 up/down: 85/-24)             Total: 61 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/hush_test/hush-misc/errexit1.tests b/shell/hush_test/hush-misc/errexit1.tests
new file mode 100755
index 0000000..7b4a156
--- /dev/null
+++ b/shell/hush_test/hush-misc/errexit1.tests
@@ -0,0 +1,5 @@
+set -e
+(true)
+echo OK
+(false)
+echo FAIL