one of the documented procedures in this installation of the ACS
vc_fetch_log   path
What it does:
Fetches the change log for a file
Defined in: /web/philip/tcl/vc-defs.tcl

Source code:

    if { [nsv_exists vc_log_cache $path] } {
	set info [nsv_get vc_log_cache $path]
	if { [lindex $info 0] == [file mtime $path] } {
	    return [lindex $info 1]
	} else {
	    # mtime has changed, kill the cache
	    nsv_unset vc_log_cache $path

    # Get the log information and cache it

    if {[catch {

	set log [vc_exec "log [vc_path_relative $path]"]

    } errmsg]} {
	ns_log Error "vc_fetch_log: $errmsg"
	set log ""

    if ![empty_string_p $log] {
	nsv_set vc_log_cache $path [list [file mtime $path] $log]

    return $log