[Log] fixes #3366: Now Logger::registerErrorHandler() accepts an argument to continue native error handler + The error <-> priority map is a public static array
CS fixes
Merge branch 'feature/3366' of git://github.com/marc-mabe/zf2 into feature/3493
[#3493] Update registerErrorHandler to return previous handler
Merge branch 'feature/3493' into develop

Close #3493
Fixes #3366