Replace curl-multi-constants with enum

[fraya]

For instance:

dylan-curl/src/lib-curl/multi/lib-curl-multi-constants.dylan

Lines 13 to 20 in d0554d3

	define constant $curlm-call-multi-perform = -1;
	define constant $curlm-ok = 0;
	define constant $curlm-bad-handle = 1;
	define constant $curlm-bad-easy-handle = 2;
	define constant $curlm-out-of-memory = 3;
	define constant $curlm-internal-error = 4;
	define constant $curlm-bad-socket = 5;
	define constant $curlm-unknown-option = 6;