Fix x-focus-frame bug with "Not an in-range integer".
* xselect.c (X_SHRT_MAX, X_SHRT_MIN, X_LONG_MAX, X_LONG_MIN)
(X_ULONG_MAX): Move these macros to xterm.h.
(x_fill_property_data): Be more generous about allowing either
signed or unsigned data of the appropriate width.
* xterm.h (x_display_set_last_user_time): New function.
All setters of last_user_time changd to use this function.
If ENABLE_CHECKING, check that the times are in range.