hush: tighten up "for" variable name check.

Add TODOs.
 Disable redir4.right part where we differ from bash.
 It is not a bug per standards.
 Add a few tests, one is in hush-bugs section:
 and_or_and_backgrounding.right. It will likely bite users
 in real world usage.

shell/hush_test/hush-vars/param_subshell.tests

@@ -7,9 +7,9 @@ echo 1=$1
 { echo 3=$3; } &
 # cant use usleep as it isnt standard in $PATH --
 # we fail when testing busybox compiled solely as "hush"
-sleep 1
+wait
 ( echo 4=$4 )
 ( echo 5=$5 ) &
-sleep 1
+wait
 true | echo 6=$6 | cat
 true | { echo 7=$7; } | cat