[fpc-pascal] Return value of StrToHostAddr and StrToHostAddr6 in sockets unit

[Noel Duffy]

While working with StrToHostAddr and StrToHostAddr6 over the past couple 
of weeks I've run into issues caused by the functions returning all zero 
addresses to indicate errors. All-zero addresses are technically valid 
according to the RFCs, so an all-zero address shouldn't be used as an 
error sentinel.

E,g:

  0.0.0.0
  ::
  ::0.0.0.0

Are considered valid if non-routable addresses. libc's inet_pton will 
successfully parse these.

A simple solution is to add functions to the sockets unit which accept a 
var record into which the output will be written and which return a 
boolean to indicate success or failure. E.g,

function inet_pton4(IP: String; var ip4: in_addr): Boolean;
function inet_pton6(IP: String; var ip6: in6_addr): Boolean;

The names I use here are the libc names, which many other languages also 
use.

Now, StrToHostAddr and StrToHostAddr6 can call the appropriate function, 
and programs that use those functions won't notice any change. But new 
code will be able to use the new functions and have an unambiguous 
answer as to whether the address is valid or not.

The change is quite straightforward to make, and it won't break existing 
code, so I think it's worthwhile to do.

Any thoughts or opinions on this?