WarcParser: Improve compatibility with ARC variants

This makes it so we can read the warcio example.arc file and the example in the ARC file format reference.

* Ignore up to 3 spurious linefeeds at the start of ARC records.
* Accept ARC records with the trailing linefeed missing.
* Accept (but currently ignore) the extra URL-record-v2 fields.
* Accept "0" in the ARC IP address field.

Fixes #82

src/org/netpreserve/jwarc/LengthedBody.java

@@ -142,7 +142,7 @@ public synchronized void consume() throws IOException {
             position += buffer.remaining();
             buffer.clear();
             if (channel.read(buffer) < 0) {
-                throw new EOFException();
+                throw new EOFException("Expected to read " + (size - position) + " more bytes");
             }
             buffer.flip();
         }