support global map-null and map-empty-string property.
add testcase for globalconfiguration
Merge branch 'master' of git://github.com/xuhuisheng/dozer into master

Conflicts:
	core/src/test/java/org/dozer/functional_tests/InvalidMappingTest.java
Merge branch 'xuhuisheng-master'
Merge pull request #62 from Spikhalsky/master

Merge pull request #24 into master