Add client_build_rev stat parameter

psiphon/server/api.go

@@ -509,6 +509,7 @@ var baseRequestParams = []requestParamSpec{
 	requestParamSpec{"sponsor_id", isHexDigits, 0},
 	requestParamSpec{"client_version", isIntString, 0},
 	requestParamSpec{"client_platform", isClientPlatform, 0},
+	requestParamSpec{"client_build_rev", isHexDigits, requestParamOptional},
 	requestParamSpec{"relay_protocol", isRelayProtocol, 0},
 	requestParamSpec{"tunnel_whole_device", isBooleanFlag, requestParamOptional},
 	requestParamSpec{"device_region", isRegionCode, requestParamOptional},

psiphon/serverApi.go

@@ -816,6 +816,7 @@ func (serverContext *ServerContext) getBaseParams() requestJSONObject {
 	// TODO: client_tunnel_core_version?
 	params["relay_protocol"] = tunnel.protocol
 	params["client_platform"] = tunnel.config.ClientPlatform
+	params["client_build_rev"] = common.GetBuildInfo().BuildRev
 	params["tunnel_whole_device"] = strconv.Itoa(tunnel.config.TunnelWholeDevice)
 
 	// The following parameters may be blank and must