Save rc stanza

Hi Michael,

The commits fixe : 

 * Handling bitmasks with more than 32 positions through an array of 32 bits bitmasks. New fko_var_bitmask_t structure. The critical_var_array table list the important variables which should not be overwritten by default.
 * The VERBOSE variable can now be added to the stanzas in fkwnoprc.
 * The fko_var_array table now contains both the position and the name of the variable.
   The table can be sorted since we have two new functions wich returns a pointer on the definition of the variables : lookup_var_by_name() and lookup_by_position()
 * When -k is used on the command line along with the --save-rc-stanza, the
   generated keys are also written in the stanza in fwknoprc.
 * ask_overwrite() : when the user inputs more than one char when prompted,
   a second call to the function does not take the second char anymore.
   We parse all of the chars until we reach an LF char and discard all of them
   except the first one.
   The overwrite is requested only when the user sets 'y', if there is anything
   else we asssume 'N'.

I have not been able to do more at this time. I send the pull request so that it is easier to track my changes.