sequencefile class now has subclassable getStream member

supports use on HDFS with pydoop
include pydoop-capable hdfs-based reader in package
Merge branch 'subclassable-stream' of coderepo1.tuk2.intelius.com:jkahn/hadoop-io-python
bugfixes to support proper HDFS reader function

better logging in reader too
Merge pull request #7 from jkahn/master

SequenceFile readers should be able to read from arbitrary files (e.g. HDFS)