Description:
------------
First of all - I marked it as feature/chamge request (not bug) bcs it`s not so 
important but maybe it`s a bug.

Official manual quote:
"The default value must be a constant expression, not (for example) a variable, a 
class member or a function call."

Code written below is correct according to the documentation but interpreter 
generate parse error: syntax error, unexpected '.', expecting ')'


function foobar($a = "abc"."def") { print($a); } //Wynik: Parse error: syntax 
error, unexpected '.', expecting ')'

Test script:
---------------
define("TEST", "abc");
 
function foo($a = TEST) { print($a); } //Res: abc
function bar($a = "def") { print($a); } //Res: def
function foobar($a = TEST."def") { print($a); } //Wynik: Parse error: syntax error, unexpected '.', expecting ')'

//abstract but also causes parse error
function foobar($a = "abc"."def") { print($a); } //Wynik: Parse error: syntax error, unexpected '.', expecting ')'