This implements a reduced variant of #1226 with just the following
change:
-Fatal error: Uncaught exception 'EngineException' with message 'Call to private method foo::bar() from context ''' in %s:%d
+Fatal error: Uncaught EngineException: Call to private method foo::bar() from context '' in %s:%d
The '' wrapper around messages is very weird if the exception
message itself contains ''. Futhermore having the message wrapped
in '' doesn't work for the "and defined" suffix of
TypeExceptions.
set_error_handler(null) and set_exception_handler(null) now return the
previous error/exception handler instead of just returning bool(true).
This is consistent with the behavior of these functions with non-null
values.
