Merge pull request #8046 from pmahoney/exceptions_as_flow_control

Replace flow-control exception with explicit test.

activesupport/lib/active_support/core_ext/file/atomic.rb

@@ -23,10 +23,10 @@ class File
     yield temp_file
     temp_file.close
 
-    begin
+    if File.exists?(file_name)
       # Get original file permissions
       old_stat = stat(file_name)
-    rescue Errno::ENOENT
+    else
       # If not possible, probe which are the default permissions in the
       # destination directory.
       old_stat = probe_stat_in(dirname(file_name))