use more efficient emptiness checking

Using empty() instead of size() can be faster. size() can take linear time but empty() is guaranteed to take constant time.
Merge pull request #49 from mscdex/master

use more efficient emptiness checking
upgrade to nan@0.2.0
upgrade to nan@0.2.1 and fix for node@0.8 compat
Quick fix for sometimes failing test
Merge branch 'master' into node_0.11_compat

Conflicts:
	src/database.cc
Merge pull request #48 from rvagg/node_0.11_compat

Initial 0.11 compatibility attempt, using new project: NAN
@0.7.0
Merge branch 'master' into less-c++

Conflicts:
	package.json
	src/database.cc
	src/leveldown.cc