Fix PHP segfault when missing function `Class::table_name`.

If the subclass is missing `Class::table_name` `__call` would be called, in turn calling `__get` which needs `Class::table_name` to work, repeat. Result is infinite recursion and a PHP segmentation fault.

**Steps to reproduce:**
1. Create class extending BasicObject
2. Don't implement `Class::table_name`
3. `$foo = new Class()`

**Expected results**
Call to undefined function Class::table_name

**Actual results**

    [Sun Feb 24 04:40:37 2013] [notice] child pid 4913 exit signal Segmentation fault (11)