py: Fix builtin hex to print prefix.

I was too hasty.  Still a one-liner though.

py/builtin.c

@@ -208,7 +208,7 @@ STATIC mp_obj_t mp_builtin_hash(mp_obj_t o_in) {
 MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_hash_obj, mp_builtin_hash);
 
 STATIC mp_obj_t mp_builtin_hex(mp_obj_t o_in) {
-    return mp_binary_op(MP_BINARY_OP_MODULO, MP_OBJ_NEW_QSTR(MP_QSTR__percent_x), o_in);
+    return mp_binary_op(MP_BINARY_OP_MODULO, MP_OBJ_NEW_QSTR(MP_QSTR__percent__hash_x), o_in);
 }
 
 MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_hex_obj, mp_builtin_hex);

py/makeqstrdata.py

@@ -17,6 +17,7 @@ codepoint2name[ord('.')] = 'dot'
 codepoint2name[ord(':')] = 'colon'
 codepoint2name[ord('/')] = 'slash'
 codepoint2name[ord('%')] = 'percent'
+codepoint2name[ord('#')] = 'hash'
 
 # this must match the equivalent function in qstr.c
 def compute_hash(qstr):

py/qstrdefs.h

@@ -107,7 +107,7 @@ Q(getattr)
 Q(globals)
 Q(hash)
 Q(hex)
-Q(%x)
+Q(%#x)
 Q(id)
 Q(io)
 Q(int)