timediff: return timediff_t from the time diff functions

... to cater for systems with unsigned time_t variables.

- Renamed the functions to curlx_timediff and Curl_timediff_us.

- Added overflow protection for both of them in either direction for
  both 32 bit and 64 bit time_ts

- Reprefixed the curlx_time functions to use Curl_*

Reported-by: Peter Piekarski
Fixes #2004
Closes #2005

1 files changed, 1 insertions, 1 deletions

diff --git a/lib/ftp.c b/lib/ftp.c
index edcfd5f80..905728778 100644
--- a/lib/ftp.c
+++ b/lib/ftp.c
@@ -351,7 +351,7 @@ static time_t ftp_timeleft_accept(struct Curl_easy *data)
     timeout_ms = other;
   else {
     /* subtract elapsed time */
-    timeout_ms -= Curl_tvdiff(now, data->progress.t_acceptdata);
+    timeout_ms -= Curl_timediff(now, data->progress.t_acceptdata);
     if(!timeout_ms)
       /* avoid returning 0 as that means no timeout! */
       return -1;