Really compute selection coordinates from buffer offset, don't assume
that row=0 col=offset is equivalent.

wsmoused: support absolute mouse position events

Tested with VirtualBox Guest Addtions.

Guess the terminal size on each change instead of during program startup.
This allows the mouse to be used properly in consoles with different sizes:
before this change it was restricted to the size reported by the console
used to start the daemon.

Problem reported by Blair Sadewitz.

branches: 1.9.4; 1.9.6;
appease gcc -Wuninitialized

Remove "bool" support for now since some platforms are still not able to
cope with it.

Call wscons mode hooks before and after generic_wscons_event. This is to
allow the selection mode hide the mouse before the device is closed, thus
fixing a minor problem (the pointer remained visible when returning from
X for some seconds).

Fix xconsole handling (enable the mouse properly when returning from X).
Closes PR bin/23223 by FUKAUMI Naoki.

Add and use the log_err, log_errx, log_warn and log_warnx functions that act as
wrappers for err, errx, warn and warnx respectively when running in foreground
and call syslog functions when running in daemon mode.
Also add and use an extra log_info function for other types of information.

- Let the main program handle multiple run modes easily. Each one is
described by a structure with pointers to functions.
- Clearly separate the "selection" mode (which provides copy and paste support
in console) from wsmoused's main program.
- Added the "modes" property to the configuration file and the "-m" command
line option to specify which modes should be activated. (this is mostly
useless for now, as only the "selection" mode exists; a new mode will
be added soon, hopefully).
- While here, several style fixes according to share/misc/style.

Fix a bug that caused the program to enter an infinite loop when selecting
an empty line.

This closes my own PR bin/19160. Reviewed by wiz.

Fix selection code [and remove trailing spaces] from Julio Merino.

PR/17402: Julio Merino: Userland portion for moused (with some changes from me).