notifications_array_serialize should use ksort with flag SORT_STRING

I have problem with compute signatures.

Function notifications_array_serialize sorts array keys for compute signature. For example i have arrays:
Array1:
'0' => 'value1' //(key as string)
'a' => 'value2'
Array2:
0 => 'value1' //(key as integer)
'a' => 'value2'

For Array1 function notifications_array_serialize generates '0,a/value1,value2'
For Array2 function notifications_array_serialize generates 'a,0/value2,value1'

To generate the same string I added SORT_STRING flag to ksort.