Minor C cleanup (#27)

* Minor C cleanup

 - some symbols can be made static:
    1. set_gov_state
    2. everything in gamemode_client.h
 - daemonize() can also take a const char*, since the name is only
   passed to printf() or syslog()
 - prevent shadowing of variables
 - use explicit (void) as parameter-list more consistently
 - use some more const.
   Move cast to more appropriate place and document that execv() behaves
   as if args where of type const *char and we trust on that.
 - example: Just use main(void), which is also an acceptable ISO-C decl
 - example: Use stderr for errors

* Fix -Wold-style-declaration issue

daemon/cpugovctl.c

@@ -40,7 +40,7 @@ POSSIBILITY OF SUCH DAMAGE.
 /**
  * Sets all governors to a value
  */
-void set_gov_state(const char *value)
+static void set_gov_state(const char *value)
 {
 	char governors[MAX_GOVERNORS][MAX_GOVERNOR_LENGTH] = { { 0 } };
 	int num = fetch_governors(governors);