585905 - ACL with targattrfilters error crashes the server
    
    https://bugzilla.redhat.com/show_bug.cgi?id=585905
    
    Bug Description:
    targattrfilters takes this format of value:
     (targattrfilters="add=attr1:F1 && attr2:F2... &&
      attrn:Fn,del=attr1:F1 && attr2:F2 ... && attrn:Fn")
    The ACL plugin code had blindly expected the value contains
    the operator "add" or "del" and '=' to concatenate the
    attribute and filter pair.  The plugin should have checked
    the possibility that the value does not follow the format.
    
    Fix Description:
    If '=' is not included in the targattrfilters value, the
    ACL parser returns ACL_SYNTAX_ERR.  Also, adding a check
    code for the returned pointer from strchr and strstr.