backlight handling:
Previously if keypad=yes was configured in LCDd.conf a value for the
backlight was sent, regardless of the configuration in hd44780-serial.c.
Now it decides upon the backlight flag from that file (enabling it in
LCDd.conf is still required). If the backlight flag indicates the device
supports backlight, the backlight_on / backlight_off values are sent (even
if they are 0x00)!
* Do not include system headers in shared files (stdlib.h).
* Don't include lcd.h only once in each driver.
* Remove some unnecessary headers from driver (e.g. syslog.h)
* Include <poll.h> instead of <sys/poll.h>
* Spelling fixes.
mmdolze