Open in split if opening normally would fail

If the user has 'hidden' turned off and the current window has
modifications, then opening with the standard ":edit" command will fail
with an error:

  E37: No write since last change (add ! to override)

So, in these cases, fall back to opening in a split, which should work
without warnings or errors.

See:

  https://wincent.com/issues/1514

Signed-off-by: Wincent Colaiuta <win@wincent.com>

ruby/command-t/controller.rb

@@ -158,8 +158,16 @@ def sanitize_path_string str
       str.gsub(/[ \\|%#"]/, '\\\\\0')
     end
 
+    def default_open_command
+      if !get_bool('&hidden') && get_bool('&modified')
+        'sp'
+      else
+        'e'
+      end
+    end
+
     def open_selection selection, options = {}
-      command = options[:command] || 'e'
+      command = options[:command] || default_open_command
       selection = sanitize_path_string selection
       VIM::command "silent #{command} #{selection}"
     end