Time parsing cleanup.

Nuke NGX_PARSE_LARGE_TIME, it's not used since 0.6.30.  The only error
ngx_parse_time() can currently return is NGX_ERROR, check it explicitly
and make sure to cast it to appropriate type (either time_t or ngx_msec_t)
to avoid signedness warnings on platforms with unsigned time_t (notably QNX).

src/mail/ngx_mail_core_module.c

diff --git a/src/mail/ngx_mail_core_module.c b/src/mail/ngx_mail_core_module.c
index 2fb537a..52a5369 100644
--- a/src/mail/ngx_mail_core_module.c
+++ b/src/mail/ngx_mail_core_module.c
@@ -479,7 +479,7 @@
                     s.len = p - s.data;
 
                     ls->tcp_keepidle = ngx_parse_time(&s, 1);
-                    if (ls->tcp_keepidle == NGX_ERROR) {
+                    if (ls->tcp_keepidle == (time_t) NGX_ERROR) {
                         goto invalid_so_keepalive;
                     }
                 }
@@ -495,7 +495,7 @@
                     s.len = p - s.data;
 
                     ls->tcp_keepintvl = ngx_parse_time(&s, 1);
-                    if (ls->tcp_keepintvl == NGX_ERROR) {
+                    if (ls->tcp_keepintvl == (time_t) NGX_ERROR) {
                         goto invalid_so_keepalive;
                     }
                 }