3.12.7: adding aufs support from git.code.sf.net/p/aufs/aufs3-standalone

NOTE: IT IS IMPORTANT TO REVIEW THE CHANGES to *mm/fremap.c* carefully, because the automatic patch of this file failed.  See below and https://altiscale.atlassian.net/browse/OPS-2746

Followed the process in this script for doing the merge:
- https://github.com/VertiCloud/dev-homes/blob/master/dineshs/alexie/includes/scripts/upgrade-prometheus.sh

Failed merge:
```
$ cat fremap.c.rej 
--- mm/fremap.c
+++ mm/fremap.c
@@ -207,11 +207,12 @@
 		 */
 		if (mapping_cap_account_dirty(mapping)) {
 			unsigned long addr;
-			struct file *file = get_file(vma->vm_file);
+			struct file *file = vma->vm_file;
 
+			vma_get_file(vma);
 			addr = mmap_region(file, start, size,
 					vma->vm_flags, pgoff);
-			fput(file);
+			vma_fput(vma);
 			if (IS_ERR_VALUE(addr)) {
 				err = addr;
 			} else {
```