Clean up warning behavior of decompression code in connection_dir_client_reached_eof()

There are several goofy things about the code that handles decompression in the above function.

First, when it decides to try two decompression methods, it logs failures from either one, even though it's only a big problem when they both fail.

Second, it treats a mismatched content-encoding as "info" when it should probably be "protocol_warn".

Third, it should be in its own function.

Fourth, the second call to warn_disallowed_anonymous_compression should probably only happen when we are about to call tor_uncompress() the second time.