hush: move towards more correct variable expansion

hush: fix a few cases in FOR v IN ... construct
      unfortunately, code growth is big - ~600 bytes

shell/hush_test/hush-bugs/quote3.right

@@ -0,0 +1,8 @@
+Testing: in $empty""
+..
+Testing: in "$*"
+.abc d e.
+Testing: in "$@"
+.abc.
+.d e.
+Finished

shell/hush_test/hush-bugs/quote3.tests

@@ -0,0 +1,12 @@
+if test $# = 0; then
+    exec "$THIS_SH" quote3.tests abc "d e"
+fi
+
+echo 'Testing: in $empty""'
+empty=''
+for a in $empty""; do echo ".$a."; done
+echo 'Testing: in "$*"'
+for a in "$*"; do echo ".$a."; done
+echo 'Testing: in "$@"'
+for a in "$@"; do echo ".$a."; done
+echo Finished