+alphanum+ is used but not defined at compile time.

[Yehouda Harpaz]

When complining util.lisp, gets an error because +alphanum+ is
undefind,unless you already loaded the file.  

That happens because +alphanum+ i used at read time inside the form 
#.(length +alphanum+) inside random-alphanumeric, and it is not
defined yet when the compiler reads the file. 

It needs to either not use it at read-time, or add eval-when (compile
load eval) around the dfeinition. 


https://github.com/spwhitton/consfigurator/blob/master/src/util.lisp