Stable7

### Steps to reproduce
1. create account ownA, ownB, ownC.
2. both ownA and ownB is one of Group 'A'.
3. login with 'ownC'. and upload one folder 'ND'. share with person 'ownA','ownB'. and logout.
4. login with 'ownB'. and share with group 'A'.
5. login with 'ownA'. folder 'ND' is duplicated.

### Expected behaviour
Tell us what should happen
if 'ownC' share file/folder with any group.
I expect that share app check the target user owned the file/folder already.
if target user owned, exclude the file/folder.

### Actual behaviour
Tell us what happens instead
I described earlier.

### Server configuration
**Operating system**:
Ubuntu14.04
**Web server:**
Apache2.4
**Database:**
Mysql5.6
**PHP version:**
PHP5.5.4
**ownCloud version:** (see ownCloud admin page)
owncloud 7.0.1
**Updated from an older ownCloud or fresh install:**

**List of activated apps:**

**The content of config/config.php:**
```
<?php
define('DEBUG',true);
$CONFIG = array (
  'trusted_domains' => 
  array (
    0 => 'localhost',
  ),
  'datadirectory' => 'C:\\Users\\SGcom\\Documents\\GitHub\\ownCloud-Core\\data',
  'dbtype' => 'mysql',
  'version' => '7.0.2.1',
  'dbname' => 'oc_data_local',
  'dbhost' => 'localhost',
  'dbtableprefix' => 'oc_',
  'dbuser' => 'oc_owncloud',
  'dbpassword' => '',
  'installed' => true,
  'custom_csp_policy' => 'default-src \'self\'; script-src \'self\' \'unsafe-eval\' \'unsafe-inline\'; style-src \'self\' \'unsafe-inline\'; frame-src *; img-src *; font-src \'self\' data:; media-src *',
  'forcessl' => false,
  'knowledgebaseenabled' => false,
  'maxZipInputSize' => 2147483648,
  'theme' => 'NCDrive',
  'maintenance' => false,
  'appstoreenabled' => false,
  'customclient_desktop' => '/agent_down.php',
);
```

**Are you using external storage, if yes which one:** local/smb/sftp/...
local
**Are you using encryption:** yes/no
no
### Client configuration
**Browser:**
Chrome37 Test
**Operating system:**
Windows8/Linux/OSX9

### Logs
#### Web server error log
```
Insert your webserver log here
```

#### ownCloud log (data/owncloud.log)
```
Insert your ownCloud log here
```

#### Browser log
```
Insert your browser log here, this could for example include:

a) The javascript console log
b) The network log 
c) ...
```
Please drop that from the PR