add the checks again.

removing these checks breaks when there is no data for any interval
fix exists check with compression
use same logic for compression

Use same logic for compression across creating files, reading from
files, and checking file existence
exclude old netty version
Merge pull request #527 from metamx/fix-empty-intervals

add filesystem checks again
Merge pull request #530 from metamx/exclude-netty

Exclude old netty version from certain dependencies
remove extra println
update docs for next rel
[maven-release-plugin] prepare release druid-0.6.105
[maven-release-plugin] prepare for next development iteration