hush: more rodust detection of unterminated strings etc;
 fix a case where we forget to copy `cmd` text;
 optimize nommu heredoc helper by not passing environment to it;
 add several tests

function                                             old     new   delta
add_till_closing_paren                               256     308     +52
parse_stream                                        2337    2378     +41
add_till_backquote                                    82     111     +29
re_execute_shell                                     269     284     +15
handle_dollar                                        802     812     +10
parse_stream_dquoted                                 316     320      +4
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 6/0 up/down: 151/0)             Total: 151 bytes

diff --git a/shell/hush_test/hush-misc/heredoc_huge.tests b/shell/hush_test/hush-misc/heredoc_huge.tests
new file mode 100755
index 0000000..c2ec281
--- /dev/null
+++ b/shell/hush_test/hush-misc/heredoc_huge.tests
@@ -0,0 +1,9 @@
+# This creates 120k heredoc
+echo 'cat <<HERE | md5sum' >"$0.tmp"
+yes "123456789 123456789 123456789 123456789" | head -3000 >>"$0.tmp"
+echo 'HERE' >>"$0.tmp"
+
+yes "123456789 123456789 123456789 123456789" | head -3000 | md5sum
+. "$0.tmp"
+rm "$0.tmp"
+echo End