py/showbc: Make printf's go to the platform print stream.

The system printf is no longer used by the core uPy code.  Instead, the
platform print stream or DEBUG_printf is used.  Using DEBUG_printf in the
showbc functions would mean that the code can't be tested by the test
suite, so use the normal output instead.

This patch also fixes parsing of bytecode-line-number mappings.

py/showbc.c

@@ -32,6 +32,9 @@
 
 #if MICROPY_DEBUG_PRINTERS
 
+// redirect all printfs in this file to the platform print stream
+#define printf(...) mp_printf(&mp_plat_print, __VA_ARGS__)
+
 #define DECODE_UINT { \
     unum = 0; \
     do { \
@@ -96,6 +99,7 @@ void mp_bytecode_print(const void *descr, const byte *ip, mp_uint_t len, const m
     #if MICROPY_PERSISTENT_CODE
     qstr block_name = code_info[0] | (code_info[1] << 8);
     qstr source_file = code_info[2] | (code_info[3] << 8);
+    code_info += 4;
     #else
     qstr block_name = mp_decode_uint(&code_info);
     qstr source_file = mp_decode_uint(&code_info);