Description:
------------
This is a minor mistake in an error message in reflectionClass.
When isSubClassOf() is given a non-existent class (X)  as a parameter the resulting fatal error says "Interface X does not exist". This should read "Class X does not exist".

Reproduce code:
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--TEST--
ReflectionClass::isSubclassOf() - non-existent class error
--FILE--
<?php
class A {}
$rc = new ReflectionClass('A');

var_dump($rc->isSubclassOf('X'));

?>
--EXPECTF--
Fatal error: Uncaught exception 'ReflectionException' with message 'Class X does not exist' in %s:5
Stack trace:
#0 %s(5): ReflectionClass->isSubclassOf('X')
#1 {main}
  thrown in %s on line 5


Expected result:
----------------
See EXPECT section above

Actual result:
--------------
Fatal error: Uncaught exception 'ReflectionException' with message 'Interface X does not exist' in %s:5