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-low.h

@@ -141,7 +141,7 @@ typedef struct hd44780_private_data {
 	// For incremental updates store last lcd contents
 	unsigned char *backingstore;
 
-	// The defineable characters
+	// The definable characters
 	CGram cc[NUM_CCs];
 	CGmode ccmode;