Add missing header prototypes

Fixes compiling errors with GCC using -Werror=missing-prototypes.

SoObjects/Appointments/MSExchangeFreeBusy.h

@@ -25,6 +25,8 @@
 
 #include <Foundation/Foundation.h>
 
+size_t curl_body_function_freebusy(void *ptr, size_t size, size_t nmemb, void *inSelf);
+
 @class MSExchangeFreeBusyResponse;
 @class MSExchangeFreeBusyView;
 

SoObjects/Appointments/SOGoWebAppointmentFolder.h

@@ -23,6 +23,8 @@
 
 #import "SOGoAppointmentFolder.h"
 
+size_t curl_body_function(void *ptr, size_t size, size_t nmemb, void *buffer);
+
 @interface SOGoWebAppointmentFolder : SOGoAppointmentFolder
 
 - (void) setUsername: (NSString *) username