follow symlinks

for people that have a symlink, such as /opt/influxdb/shared/data as a link to a datadir on a different volume, this makes sure the ownership is reset there too.
otherwise you can get influxdb to panic due to incorrect permissions (happened to me)
Merge pull request #651 from Dieterbe/patch-1

follow symlinks
update the changelog

[skip ci]
Fix influxdb on 32 bit arch
Fix a typo

[skip ci]
Close #643. Support pretty-print of JSON via HTTP API
Abstract storage engines

This commit create a storage engine interface and modify shards to use
interface instead. It also adds a B-Tree implementation and benchmark
tool to compare the performance of the different storage engines.
Make the storage engine selectable from the config file
Remove LevelDb from the shard and the shard data store
keep track of the database type
Add support for rocksdb
Add support for hyperleveldb
fix the timing of the second write
Don't close the cache which could still be used
fix the makefile
fix the directory