Ensure POST request gets normalized data

    Normalization only happens after potentially sending a request to the
    backend. This generates hard to debug errors when descisions are made
    based on these variables that affects application behaviors.
    
    For example, if one of the normalized values is used to select a
    different storeview, then sending off the request prematurely causes the
    wrong storeview to be selected.
    
    Therefore we move all normalization to the earliest stage in vcl_recv
    and it should remain before any `return(pipe)` statement is made, unless
    explicitly documented why it's safe to deviate from the straight and
    narrow.