[wishlist] avoid empty statements in shell scripts

[Roland Illig]

Hi,

I sometimes get ./configure scripts that have a syntax error near an 
`else'. The reson for this is that some shells don't like

    if true; then
    else
    fi

Instead they expect

    if true; then
      :
    else
      :
    fi

The first code is often generated by a statement like

AC_CHECK_LIB([l], [main], [], [])

I see two possible solutions:

1. replace empty ACTION-IF-* by `:'
2. warn the user about it

What do you think about it?

Roland