fix(review): address PR #130 review

- proftest: declare the _mkdir_recursive loop index inside the for.
- xmpp/presence: shorten the resource-snapshot comment to one line.
- command/cmd_funcs: report the /vcard remove index error via cons_show_error.
- common: replace g_assert in g_diff_to_gsize with a log_error + return 0
  (moved out of the header into common.c); take get_random_string length as
  size_t instead of asserting non-negative.
- otr: drop the change-narrating comment on the whitespace memmove.

Refs #112

tests/functionaltests/proftest.c

@@ -119,10 +119,9 @@ _create_dir(const char* name)
 gboolean
 _mkdir_recursive(const char* dir)
 {
-    size_t i;
     gboolean result = TRUE;
 
-    for (i = 1; i <= strlen(dir); i++) {
+    for (size_t i = 1; i <= strlen(dir); i++) {
         if (dir[i] == '/' || dir[i] == '\0') {
             gchar* next_dir = g_strndup(dir, i);
             result = _create_dir(next_dir);