Get a rid of missing annotation warnings.
Shortcut for VectorGroup#add method if single vector key is required.
Unify API for Frame#add to return reference to this frame.
Fixed NPE in Frame#find, Frame#add calls when frame is empty.
Test for PUB-216.

The test exposes corner case when TransfVec is taking
minimum from underlying vector to perform transformation but
minimum does not reflect vector enum domain.
Fix compilation problem caused by a stupid bug in javac6

Javac 6 does not handle overloaded methods properly.
Two methods:
int [] ar(int ...a)
long[] ar(long...a)
are detected as ambiguous :-(

See bug:
http://bugs.java.com/view_bug.do;jsessionid=a1a7fa712aad9e86f7d2fdf7ad6af?bug_id=6199075
Fix for PUB-216 - bad confusion matrix.

The TransfVec implementation use a proper
bijection between underlying vector values and
transformed values.

The bijection is implemented by a dummy hash map based
on two arrays - one for holding vector domain, one for holding
transformed values. The value search is based on binary search.
Here the next step will be to put proper hash function (simple one like
Cuckoo hashing).
Merge branch 'master' of github.com:0xdata/h2o