fixes build issue with zaptel

(closes issue 0017394)
Reported by: aragon
Patches:
      half_buffer_fix.diff uploaded by dvossel (license 671)
Tested by: aragon


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.6.2@265615 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_dahdi.c

@@ -5071,8 +5071,10 @@ static int parse_buffers_policy(const char *parse, int *num_buffers, int *policy
 		*policy = DAHDI_POLICY_WHEN_FULL;
 	} else if (!strcasecmp(policy_str, "immediate")) {
 		*policy = DAHDI_POLICY_IMMEDIATE;
+#ifdef DAHDI_POLICY_HALF_FULL
 	} else if (!strcasecmp(policy_str, "half")) {
 		*policy = DAHDI_POLICY_HALF_FULL;
+#endif
 	} else {
 		ast_log(LOG_WARNING, "Invalid policy name given '%s'.\n", policy_str);
 		return -1;