Fixing user can't delete his own message in case username != full 
name in OC.

description:
lib/conversations.php[line 235]:
PreparePost returns $author = user display name.

part.conversation.php[line 19]:
if( USER_CONVERSATIONS_CAN_DELETE && ( 
OC_User::isAdminUser($uid) || $author == $uid ) ):

$author != $uid because the user display name is different then 
his username.
Example [add user in OC]:
username: shachar fullname:Shachar Ochyon
Merge pull request #30 from ShacharOch/fix_user_delete

Fixing user can't delete his own message if fullname != username