Header fixes:

* 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.

server/drivers/hd44780-usblcd.h

@@ -2,7 +2,6 @@
 #define HD_USBLCD_H
 
 #include "lcd.h"			  /* for lcd_logical_driver */
-#include "hd44780-low.h"		  /* for HD44780_functions */
 
 // initialise this particular driver
 int hd_init_usblcd(Driver *drvthis);