Scripts in browser don't wait for async script to finish

[jcubic]

When scripts are executed and don't wait for the previous script to finish.
This is a problem when bootstrapping, the second script doesn't have a standard library because the bootstrap script runs async.

example:

<script type="text/x-scheme" bootstrap>
    (console.log "1")
</script>
<script type="text/x-scheme">
    (console.log "2")
    (--> console (log "3"))
</script>

the output:

2
--> is not defined
1