Fix revlog-ng interaction with old-http.
revlog.py wasn't trying to detect the version of a revlog file that
doesn't exist on the filesystem (as is the case with old-http).
Additionally, there was an off-by-one error in httprangereader.read
(ranges in HTTP Range headers are inclusive), making it get more data
than what was asked for. This made a struct.unpack complain that
"unpack str size does not match format".
Finally, with the two fixes above, test-static-http fails, since
BaseHTTPServer doesn't understand ranges and returns too much data.
Work around that by reading only the specified amount.
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