free: instead of Curl_safefree()

Since we just started make use of free(NULL) in order to simplify code,
this change takes it a step further and:

- converts lots of Curl_safefree() calls to good old free()
- makes Curl_safefree() not check the pointer before free()

The (new) rule of thumb is: if you really want a function call that
frees a pointer and then assigns it to NULL, then use Curl_safefree().
But we will prefer just using free() from now on.

lib/imap.c

@@ -547,8 +547,8 @@ static CURLcode imap_perform_login(struct connectdata *conn)
   result = imap_sendf(conn, "LOGIN %s %s", user ? user : "",
                       passwd ? passwd : "");
 
-  Curl_safefree(user);
-  Curl_safefree(passwd);
+  free(user);
+  free(passwd);
 
   if(!result)
     state(conn, IMAP_LOGIN);
@@ -661,7 +661,7 @@ static CURLcode imap_perform_list(struct connectdata *conn)
     /* Send the LIST command */
     result = imap_sendf(conn, "LIST \"%s\" *", mailbox);
 
-    Curl_safefree(mailbox);
+    free(mailbox);
   }
 
   if(!result)
@@ -702,7 +702,7 @@ static CURLcode imap_perform_select(struct connectdata *conn)
   /* Send the SELECT command */
   result = imap_sendf(conn, "SELECT %s", mailbox);
 
-  Curl_safefree(mailbox);
+  free(mailbox);
 
   if(!result)
     state(conn, IMAP_SELECT);
@@ -777,7 +777,7 @@ static CURLcode imap_perform_append(struct connectdata *conn)
   result = imap_sendf(conn, "APPEND %s (\\Seen) {%" CURL_FORMAT_CURL_OFF_T "}",
                       mailbox, conn->data->state.infilesize);
 
-  Curl_safefree(mailbox);
+  free(mailbox);
 
   if(!result)
     state(conn, IMAP_APPEND);
@@ -1800,7 +1800,7 @@ static CURLcode imap_sendf(struct connectdata *conn, const char *fmt, ...)
   result = Curl_pp_vsendf(&imapc->pp, taggedfmt, ap);
   va_end(ap);
 
-  Curl_safefree(taggedfmt);
+  free(taggedfmt);
 
   return result;
 }
@@ -2031,7 +2031,7 @@ static CURLcode imap_parse_url_path(struct connectdata *conn)
     /* Decode the value parameter */
     result = Curl_urldecode(data, begin, ptr - begin, &value, &valuelen, TRUE);
     if(result) {
-      Curl_safefree(name);
+      free(name);
       return result;
     }
 
@@ -2070,14 +2070,14 @@ static CURLcode imap_parse_url_path(struct connectdata *conn)
       value = NULL;
     }
     else {
-      Curl_safefree(name);
-      Curl_safefree(value);
+      free(name);
+      free(value);
 
       return CURLE_URL_MALFORMAT;
     }
 
-    Curl_safefree(name);
-    Curl_safefree(value);
+    free(name);
+    free(value);
   }
 
   /* Does the URL contain a query parameter? Only valid when we have a mailbox