Time parsing cleanup.

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).