VS2010 build: Prepare compat/jansson-2.5.

Cherry-picked by veox.

Not a big fan of modifying compat libraries, makes it harder to maintain
later on. See if these changes are relevant upstream.

compat/jansson-2.5/src/load.c

@@ -365,7 +365,7 @@ static void lex_scan_string(lex_t *lex, json_error_t *error)
          - two \uXXXX escapes (length 12) forming an UTF-16 surrogate pair
            are converted to 4 bytes
     */
-    lex->value.string = jsonp_malloc(lex->saved_text.length + 1);
+    lex->value.string = (char *)jsonp_malloc(lex->saved_text.length + 1);
     if(!lex->value.string) {
         /* this is not very nice, since TOKEN_INVALID is returned */
         goto out;

compat/jansson-2.5/src/memory.c

@@ -41,7 +41,7 @@ char *jsonp_strdup(const char *str)
     if(len == (size_t)-1)
         return NULL;
 
-    new_str = jsonp_malloc(len + 1);
+    new_str = (char *)jsonp_malloc(len + 1);
     if(!new_str)
         return NULL;
 

compat/jansson-2.5/src/strbuffer.c

@@ -23,7 +23,7 @@ int strbuffer_init(strbuffer_t *strbuff)
     strbuff->size = STRBUFFER_MIN_SIZE;
     strbuff->length = 0;
 
-    strbuff->value = jsonp_malloc(strbuff->size);
+    strbuff->value = (char *)jsonp_malloc(strbuff->size);
     if(!strbuff->value)
         return -1;
 
@@ -86,7 +86,7 @@ int strbuffer_append_bytes(strbuffer_t *strbuff, const char *data, size_t size)
         new_size = max(strbuff->size * STRBUFFER_FACTOR,
                        strbuff->length + size + 1);
 
-        new_value = jsonp_malloc(new_size);
+        new_value = (char *)jsonp_malloc(new_size);
         if(!new_value)
             return -1;
 

compat/jansson-2.5/src/value.c

@@ -229,7 +229,7 @@ const char *json_object_iter_key(void *iter)
     if(!iter)
         return NULL;
 
-    return hashtable_iter_key(iter);
+    return (char *)hashtable_iter_key(iter);
 }
 
 json_t *json_object_iter_value(void *iter)