move cache dir to sites/example.com/files/html_cache

This thread aims to get the best of:

1. This newer one #349373: Replace file_put_contents with file_save_data

2. The old issue #223610: Race condition in cache file creation

and close them both.

In both issues above the proposed solutions are similar.

old issue:

+      $tempfile = $filename . getmypid();
+      if (file_put_contents($tempfile, $data) === FALSE) {
+        watchdog('boost', t('Unable to write file: %file', array('%file' => $tempfile)), WATCHDOG_WARNING);
+      } else {
+        // put the temp file in its final location
+        if (rename($tempfile,$filename) === FALSE) {
+          watchdog('boost', t('Unable to rename file: %file', array('%file' => $tempfile)), WATCHDOG_WARNING);
+        }

new issue uses : (with the problem that we need to set our cache to be in the drupal file system (where images are etc...) )

function file_save_data($data, $dest, $replace = FILE_EXISTS_RENAME) {
  $temp = file_directory_temp();
  // On Windows, tempnam() requires an absolute path, so we use realpath().
  $file = tempnam(realpath($temp), 'file');
  if (!$fp = fopen($file, 'wb')) {
    drupal_set_message(t('The file could not be created.'), 'error');
    return 0;
  }
  fwrite($fp, $data);
  fclose($fp);

  if (!file_move($file, $dest, $replace)) {
    return 0;
  }

  return $file;
}

I am actually a fan of the second one - let me explain:

till now we were accustomed that boost keeps caches in :

cache/example.com/

What if we turn this on its head and make boost keep caches in:

sites/default/files/html_cache (default site)
sites/example.com/html_cache (multisite instance)

thus :

1. we eliminate the need for an explicit set ting in the UI (less work for the user that sets up)
2. can use the drupal_file_save func safely
3. we are still multisite aware ...

So?