Remove unused makefile vars
Use rocksdb in the data test suite
add trace to the available logging levels
Add some trace logging
Fill even when no points exists in the given time range

Fix #996. Close #1067
Add func to get str desc of Processor chain

Close #1068
Revert "Use rocksdb in the data test suite" (info below)

This reverts commit 49c49d818c5ecb87fb5bd6f6066850251f3c303e.

In order to use rocksdb we need g++ >= 4.7 (which has support for
C++0x11). It's too expensive to build g++ every time. Upgrading the
ubuntu distro used by travis seems to be coming soon, I'll shelf this
for now until travis-ci/travis-ci#2046 is resolved.
Fix the timestamps set by the collectd plugin

Timestamps should be in microseconds instead of milliseconds.

Fix #1075. Close #1076
Fix #943: don't try to take 2 snapshots at a time