opStrategy and ordering for ArithmeticPostAgg

Fixes #510
Add HdfsTaskLogs
refactor docs for histograms
make histos work with groupby maybe
Druid Fireshose

Add druidFirehose, can be used to reIndex filtered data from a
datasource
fix examples start port
AWSCredentialsProvider for s3-extentions

- fileSessionCredentials property is added
- AWSSessionCredentialsAdapter is adapter class between aws sdk AWSCredentialsProvider to jets3t Credentials
- FileSessionCredentialsProvider will refresh its session credentials from the file
- S3StorageDruidModule should return different AWSCredentialsProvider on the config settings
A few fixes

- EasyMock instead of Mockito
- FileSessionCredentialsProvider fields should be volatile
- getRestS3Service should create AWSCredentials not a AWSSessionCredentials with fixed credentials
improve port finding strategy for task runner

1) Recycle free ports
2) Choose only ports that are free & not used by any other application
Merge pull request #630 from metamx/port-finder

improve port finding strategy for task runner
fix broken rename of rejection policies
Merge branch 'master' of github.com:metamx/druid
License header and utf-8
review comments

1) Rename firehose to IngestSegment
2) fix segment overlapping, intervals
3) fix overshadow
Merge pull request #618 from realfun/master

Add HdfsTaskLogs
Remove redundant forking task runner config
update refresh manually every hour
Add ShardSpec Lookup

Optimize choosing shardSpec for Hash Partitions
CombiningFirehoseFactory

can be used to ingest data from multiple sources.
Use Ingest task instead of Noop Task