According to the discussion in Krakow with @mbabker we can't namespace the fields in libraries/joomla in the 3 series, because of autoloading. So this pr should be targeted against the 4.0-dev branch.
The two in libraries/legacy are fine to do for 3.8. But the rest in libraries/joomla have to wait for 4.0 since the directory they are in now is not autoloaded and this move would make the classes autoloaded and we've already run into problems with duplicated classes from the core field offerings.
According to the discussion in Krakow with @mbabker we can't namespace the fields in libraries/joomla in the 3 series, because of autoloading. So this pr should be targeted against the 4.0-dev branch.