fix "can't convert Errno::EACCES into String" in case of no permission of public/plugin_assets on Ruby 1.9.3 (#11945)

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@10471 e93f8b46-1217-0410-a6f0-8f06a7374b81

lib/redmine/plugin.rb

@@ -346,7 +346,7 @@ module Redmine #:nodoc:
         begin
           FileUtils.mkdir_p(target_dir)
         rescue Exception => e
-          raise "Could not create directory #{target_dir}: \n" + e
+          raise "Could not create directory #{target_dir}: " + e.message
         end
       end
 
@@ -357,7 +357,7 @@ module Redmine #:nodoc:
             FileUtils.cp(file, target)
           end
         rescue Exception => e
-          raise "Could not copy #{file} to #{target}: \n" + e
+          raise "Could not copy #{file} to #{target}: " + e.message
         end
       end
     end