wget: code shrink by splitting main() into easier-to-optimize functions

wget: code shrink by splitting main() into easier-to-optimize functions

function                                             old     new   delta
retrieve_file_data                                     -     356    +356
wget_main                                           2793    2326    -467
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(add/remove: 1/0 grow/shrink: 0/1 up/down: 356/-467)         Total: -111 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>