Cleanup I2C handling

* Move OS specific code to new files i2c.h and i2c.c
* As side effect a likely bug (linux only code) in the existing driver
  has been fixed.

Compile tested on Debian/i386 and OpenWRT/arm.

Signed-off-by: Harald Geyer <harald@ccbib.org>

server/drivers/hd44780-low.h

@@ -29,6 +29,8 @@
 # include <ftdi.h>
 #endif
 
+#include "i2c.h"
+
 /** \name Symbolic names for connection types
  *@{*/
 #define HD44780_CT_UNKNOWN		0
@@ -157,7 +159,7 @@ typedef struct hd44780_private_data {
 #endif
 
 #ifdef HAVE_I2C
-	/* libi2c-based connection types */
+	/* i2c based connection types */
 	
 	int i2c_backlight_invert;
 	int i2c_line_RS;
@@ -169,6 +171,7 @@ typedef struct hd44780_private_data {
 	int i2c_line_D6;
 	int i2c_line_D7;
 
+	I2CHandle *i2c;
 #endif
 
 #ifdef WITH_ETHLCD