[TAP] fix after merge branch 'whiteknight/io_cleanup1'

$ ./parrot-prove -v t/op/string_cs.t
t/op/string_cs.t .. Malformed UTF-8 string

current instr.: 'parrot;TAP;Parser;file' pc 2101 (runtime/parrot/library/TAP/Parser.pir:914)
called from Sub 'parrot;TAP;Harness;aggregate_tests' pc 330 (runtime/parrot/library/TAP/Harness.pir:132)
called from Sub 'parrot;TAP;Harness;runtests' pc 235 (runtime/parrot/library/TAP/Harness.pir:107)
called from Sub 'do' pc 225 (runtime/parrot/bin/prove.pir:147)

runtime/parrot/library/TAP/Parser.pir

@@ -910,15 +910,18 @@ C<TAP;Parser> is designed to produce a proper parse of TAP output.
     push_eh _handler
     $P0.'open'(filename, 'r')
     pop_eh
-    $P0.'encoding'('utf8')
+    $P0.'encoding'('binary')
     $S0 = $P0.'readline'()
+    $I0 = find_encoding 'utf8'
+    $S0 = trans_encoding $S0, $I0
     $I0 = index $S0, '#!'
     unless $I0 == 0 goto L1
     $P0.'close'()
     $S0 = _get_exec($S0)
     .tailcall self.'exec'($S0, filename)
   L1:
     $P0.'seek'(0, 0)
+    $P0.'encoding'('utf8')
     setattribute self, 'stream', $P0
     .return ()
   _handler: