Description:
------------
Accessing a character of a string using the deprecated 
array notation when the array index is not a number does 
not produce a notice or warning, but I believe it 
should.

If I write $test['some string'] = '234' what I probably 
want to do is to have $test be an array with a key 
'some string' and a value '234', but if $test was 
already a string, PHP instead sets character index 0 of 
the string to "2". PHP should issue an error of some 
kind, alerting the programmer that $test is being used 
as a string, so that the programmer can properly 
initialize the array with $test = array() before filling 
it.

Reproduce code:
---------------
$test = 'blah';

$test[2] = 'x';
// sets the third character of $test to "x"

echo $test . "<br />\n";
// outputs "blxh"

$test['some string'] = '234';
// sets the first character of $test to "2"

echo $test . "<br />\n";
// outputs "2lxh"

Expected result:
----------------
Warning: invalid non-numeric index into string $test