Do not display rmagick exception in I18n message

For instance, if you upload a text file with a JPG extension, rmagick generate an exception, whose message contains the full path of your project directory. It seems to me that it's a security issue, since the generated message displayed to the frontoffice user contains the server project directory.
I didn't test other cases (for the orher messages), but potentially this problem can appear somewhere else
Merge pull request #1361 from manuelpradal/patch-1

Do not display rmagick exception in I18n message