text? has been removed from Column class

Detail can be found here: https://github.com/rails/rails/commit/d44702ee45219153c5e56da0a06ffe6ab5d14518

So writing a CLOB column might causing error in 4.2 beta 1. Looks we don't need this check any longer, simply check it against String type might do the job.
Merge pull request #487 from pzgz/rails42

text? has been removed from Column class