Unset mode when clearing regions

tclearregion() was clearing regions using spaces and the current
attributes of the terminal. It was correct with all the modes excepct
underline, because they didn't affect the space character, but in
the case of underline it was a problem. A easy way of seeing this
problem is writing this in the last line of the terminal:

	tput smul ; echo first; tput rmul; echo second; echo third

Fist was underlined, and second and third were not underlined, but
the spaces at the right of second was underlined becuause in the
previous scrool underline mode was set.
Remove ul capability

This capability indicates that underscore '_' overstrike current
letter under the cursor. It means that you can generate a
underline 'b' using 'b^H_', because it writes a 'b' then backward
one characther and then overstrike '_'. St has not such behaviour,
so it is an error to have this capability.
tresize return value is not used

Signed-off-by: Roberto E. Vargas Caballero <k0ga@shike2.com>
Don't set dirty all lines because tswapcreen do it

Signed-off-by: Roberto E. Vargas Caballero <k0ga@shike2.com>
Fix portability problem in techo()

ISCONTROL chechks if a value is between 0 and 0x1f or
between 0x80 and 0x9f. Char signess depends of architecture
and compiler, so in some environment the second case is
always false (and wrong), Techo() calls ISCONTROL with a
char variable, whose type cannot be changed because tpuc()
expects a pointer to char, so the solution is to insert a
cast in the call to ISCONTROL.
Convert VT102ID to a config variable

VT102ID is the sequence that the terminal returns when it is inquired
to identify itself. This value should be configurable in the same
way that another st parameters.
Port to wayland