Make it clear which functions that are intended to be translation unit local

Do not share functions that are meant to be translation unit local with
other translation units. Use internal linkage for those consistently.

src/bitcoind.cpp

@@ -40,7 +40,7 @@
  * Use the buttons <code>Namespaces</code>, <code>Classes</code> or <code>Files</code> at the top of the page to start navigating the code.
  */
 
-void WaitForShutdown()
+static void WaitForShutdown()
 {
     while (!ShutdownRequested())
     {
@@ -53,7 +53,7 @@ void WaitForShutdown()
 //
 // Start
 //
-bool AppInit(int argc, char* argv[])
+static bool AppInit(int argc, char* argv[])
 {
     bool fRet = false;