GH-125: error out if a file goes/is missing when we load it
"Urls" submenu of the main menu

(Forgive me, I'm sick.)
Escape the urls, and add &unique anchors
GH-129: If a path is absolute, don't escape its drive-letter colon
GH-135: About, not Cancel, shown when we have Help

This, annoyingly, breaks cancelling the dialog with the escape key.
Should this work?  Probably.  Annoying.  Very annoying.  I'm not so
concerned about the problem, as I don't think the help is useful, modern
or actually wanted by most people using it.

Cancellation works by:
 * ssd->cancelbutton->button.iscancel = TRUE;
 * if (ctrl->button.iscancel) actual_base_id = IDCANCEL;
 * When someone presses escape, Windows generates a WM_COMMAND(IDCANCEL)
  * This is not documented anywhere sensible.  Nowhere.  NOWHERE.

Maybe we could hijack the WM_COMMAND before it arrives at the button
handler, or something?  Shrug.
GH-136: load host in adb sessions
GH-133: Crash on initial connection fail (serial)

I knew that would go wrong.  Dammit.

Re-review that code for possible horrors.  I'm still not happy with
backhandle possibly being junk, but nothing should really get far enough
to notice (famous last words).  Still going with it being better to run
stuff, than to not run it.
GH-131: Ignore folders while fetching file sessions

While fetching session list from files, ignore folders and fetch next
available session file instead of returning null.

If you happen to have a stray folder in the sessions folder, then the
order in which FindNextFile() gets files is uncertain. And often we end up
seeing a folder traversed in the middle of several session files.

This issue is easily reproducable if we have lots of session files that
start with different names and a folder.
Merge branch 'master' into feature