Replace almost all uses of enum connection_state with struct
connection_status. This removes the assumption that errno values used
by the system are between 0 and 100000. The GNU Hurd uses values like
ENOENT = 0x40000002 and EMIG_SERVER_DIED = -308.
This commit is derived from my attachments 450 and 467 to bug 1013.
Until the last change in src/ecmascript/see/window.c, the two copies
of delayed_goto_uri_frame in src/ecmascript/spidermonkey/window.c and
in src/ecmascript/see/window.c were identical. That change applies to
both versions, so move the newer one to src/session/task.c and eliminate
the duplication. Also move struct delayed_open to src/session/session.h.
