move from avro namespace to internal_avro namespace

so symbols don't collide. You can freely use sed to replace internal_avro with another string, all matches are valid to change.
replace uses of std::auto_ptr with boost::shared_ptr

- auto_ptr triggers deprecation warnings in some compilers
- boost::shared_ptr allows, for example memoryOutputStreams to be passed to something and then their contents still accessed when done
fix compilation on mac os 10.9
remove extra AVRO_DECL in .cc file
add patch to enable seeks in DataFileReader

This allows you to go to any block in constant time.
add the ability to have DataFiles in arbitrary streams

for example, memory buffers or gzipped stream.
add test of gzipping a DataFile