py/builtinimport: Support importing packages from compiled .mpy files.

This patch ensures that __init__.mpy files are imported if their
containing directory is imported as a package.

py/builtinimport.c

@@ -73,15 +73,8 @@ STATIC mp_import_stat_t mp_import_stat_any(const char *path) {
     return mp_import_stat(path);
 }
 
-STATIC mp_import_stat_t stat_dir_or_file(vstr_t *path) {
+STATIC mp_import_stat_t stat_file_py_or_mpy(vstr_t *path) {
     mp_import_stat_t stat = mp_import_stat_any(vstr_null_terminated_str(path));
-    DEBUG_printf("stat %s: %d\n", vstr_str(path), stat);
-    if (stat == MP_IMPORT_STAT_DIR) {
-        return stat;
-    }
-
-    vstr_add_str(path, ".py");
-    stat = mp_import_stat_any(vstr_null_terminated_str(path));
     if (stat == MP_IMPORT_STAT_FILE) {
         return stat;
     }
@@ -97,6 +90,18 @@ STATIC mp_import_stat_t stat_dir_or_file(vstr_t *path) {
     return MP_IMPORT_STAT_NO_EXIST;
 }
 
+STATIC mp_import_stat_t stat_dir_or_file(vstr_t *path) {
+    mp_import_stat_t stat = mp_import_stat_any(vstr_null_terminated_str(path));
+    DEBUG_printf("stat %s: %d\n", vstr_str(path), stat);
+    if (stat == MP_IMPORT_STAT_DIR) {
+        return stat;
+    }
+
+    // not a directory, add .py and try as a file
+    vstr_add_str(path, ".py");
+    return stat_file_py_or_mpy(path);
+}
+
 STATIC mp_import_stat_t find_file(const char *file_str, uint file_len, vstr_t *dest) {
 #if MICROPY_PY_SYS
     // extract the list of paths
@@ -463,7 +468,7 @@ mp_obj_t mp_builtin___import__(size_t n_args, const mp_obj_t *args) {
                     mp_store_attr(module_obj, MP_QSTR___path__, mp_obj_new_str(vstr_str(&path), vstr_len(&path), false));
                     vstr_add_char(&path, PATH_SEP_CHAR);
                     vstr_add_str(&path, "__init__.py");
-                    if (mp_import_stat_any(vstr_null_terminated_str(&path)) != MP_IMPORT_STAT_FILE) {
+                    if (stat_file_py_or_mpy(&path) != MP_IMPORT_STAT_FILE) {
                         vstr_cut_tail_bytes(&path, sizeof("/__init__.py") - 1); // cut off /__init__.py
                         //mp_warning("%s is imported as namespace package", vstr_str(&path));
                     } else {