Generate #defines for initializing message structures.

Usage like:
MyMessage foo = MyMessage_init_default;

MyMessage_init_default will initialize to default values defined in .proto.

MyMessage_init_zero will initialize to null/zero values. Same results as {}
or {0}, but will avoid compiler warnings by initializing everything explicitly.

Update issue 79
Status: FixedInGit

tests/alltypes/decode_alltypes.c

@@ -19,7 +19,8 @@
    the decoding and checks the fields. */
 bool check_alltypes(pb_istream_t *stream, int mode)
 {
-    AllTypes alltypes;
+    /* Uses _init_default to just make sure that it works. */
+    AllTypes alltypes = AllTypes_init_default;
     
     /* Fill with garbage to better detect initialization errors */
     memset(&alltypes, 0xAA, sizeof(alltypes));

tests/alltypes/encode_alltypes.c

@@ -13,7 +13,7 @@ int main(int argc, char **argv)
     int mode = (argc > 1) ? atoi(argv[1]) : 0;
     
     /* Initialize the structure with constants */
-    AllTypes alltypes = {0};
+    AllTypes alltypes = AllTypes_init_zero;
     
     alltypes.req_int32         = -1001;
     alltypes.req_int64         = -1002;