Merge of r4968, r4969, r4977, r4980, r4981, r4990: geo fixes.

Merge of r4968, r4969, r4977, r4980, r4981, r4990: geo fixes.

*) Geo: improved ngx_http_geo_block() code readability.

*) Geo: fixed the "ranges" without ranges case.  The following
   configuration returned an empty value for $geo:

       geo $geo {
           ranges;
           default default;
       }

*) Fixed return type of internal function that allocates radix tree nodes.

*) There's no need to normalize address returned by ngx_ptocidr().

*) Geo: ensure that default entry is always present.  If 0.0.0.0/32 entry
   was present and there was no explicit "default", we failed to add an
   empty string as a default value.

*) Trailing whitespace fix.