Eric Landes provided the patch (edited by me) that introduces the --keepalive-time to curl to set the keepalive probe interval. I also took the opportunity to rename the recently added no-keep-alive option to no-keepalive to keep a consistent naming and to avoid getting two dashes in these option names. Eric also provided an update to the man page for the new option. 
diff --git a/RELEASE-NOTES b/RELEASE-NOTES index 49f540f..b1d41c1 100644 --- a/RELEASE-NOTES +++ b/RELEASE-NOTES 
@@ -1,7 +1,7 @@  Curl and libcurl 7.18.0    Public curl releases: 103 - Command line options: 125 + Command line options: 126  curl_easy_setopt() options: 150  Public functions in libcurl: 56  Public web site mirrors: 42 @@ -12,12 +12,13 @@    o --data-urlencode  o CURLOPT_PROXY_TRANSFER_MODE - o --no-keep-alive - now curl does connections with keep-alive enabled by + o --no-keepalive - now curl does connections with keep-alive enabled by  default  o --socks4a added (proxy type CURLPROXY_SOCKS4A for libcurl)  o --socks5-hostname added (CURLPROXY_SOCKS5_HOSTNAME for libcurl)  o curl_easy_pause()  o CURLOPT_SEEKFUNCTION and CURLOPT_SEEKDATA + o --keepalive-time    This release includes the following bugfixes:   @@ -72,6 +73,6 @@  Emil Romanus, Alessandro Vesely, Ray Pekowski, Spacen Jasset, Andrew Moise,  Gilles Blanc, David Wright, Vikram Saxena, Mateusz Loskot, Gary Maxwell,  Dmitry Kurochkin, Mohun Biswas, Richard Atterer, Maxim Perenesenko, - Daniel Egger, Jeff Johnson, Nikitinskit Dmitriy, Georg Lippitsch + Daniel Egger, Jeff Johnson, Nikitinskit Dmitriy, Georg Lippitsch, Eric Landes    Thanks! (and sorry if I forgot to mention someone)