Several long-time production-tested syntax fixes

Breaking commit: 137ced89

Original issue: http://bugs.dwoo.org/dwoo/bugs/issue/92

Original issue: http://bugs.dwoo.org/dwoo/bugs/issue/89

Original issue: http://bugs.dwoo.org/dwoo/bugs/issue/88

Original issue: http://bugs.dwoo.org/dwoo/bugs/issue/30

Fixed Dwoo compiler to not unnecessarily fail at statements involving method calls and multiple arguments

Previously a Dwoo_Compilation_Exception was thrown on statements like
"{$a = $myObj->myMethod($myObj2->getId(), true)}" – they were actually
running fine though

Fix for reading unassigned _filter from Zend_View_Abstract

Added support for nested blocks for template inheritance, block names must be unique, overriding of any block is done at the top level. Fixes #7