Description:
------------
According to the manual, ob_get_flush() and ob_end_flush() should fail if PHP_OUTPUT_HANDLER_FLUSHABLE was not given during ob_start(). That seems like a sensible policy, but the flag is only checked during ob_flush().

I noticed this bug while reading output.c, I don't actually use those functions.

Test script:
---------------
<?php
ob_start(null, 0, PHP_OUTPUT_HANDLER_REMOVABLE);
print "x\n";
var_dump(ob_get_flush());


Expected result:
----------------
PHP Notice:  ob_get_flush(): failed to flush buffer of default output handler (0) in ob_get_flush.php on line 4
bool(false)
x

Actual result:
--------------
x
string(2) "x
"