Fix some warnings, leave note about single-client tools

Signed-off-by: falkTX <falktx@falktx.com>

Author: falkTX

README

@@ -62,6 +62,4 @@ Unless compiled with GCC 3.3 or later, jack_interposer only works for
 single-CPU machines, or machines configured to run the application under test 
 on a single CPU.
 
-== Related applications ==
-
-http://trac.jackaudio.org/wiki/WalkThrough/Dev/Tools
+This tool only works for single-client applications.

jack_interposer.c

@@ -37,9 +37,9 @@ bool THREAD_LOCAL in_rt = false;
 #include "checkers.c"
 #include "manual.c"
 
-JackProcessCallback real_process_callback;
+static JackProcessCallback real_process_callback;
 
-int interposed_process_callback(jack_nframes_t nframes, void* arg)
+static int interposed_process_callback(jack_nframes_t nframes, void* arg)
 {
   int result;
 
@@ -55,7 +55,7 @@ int interposed_process_callback(jack_nframes_t nframes, void* arg)
 int jack_set_process_callback(jack_client_t* client,
 	JackProcessCallback process_callback, void* arg)
 {
-  static int (*func)() = NULL;
+  static int (*func)(jack_client_t*, JackProcessCallback, void*) = NULL;
   int result;
 
   if (getenv("JACK_INTERPOSER_NO_ABORT") != NULL)
@@ -64,7 +64,7 @@ int jack_set_process_callback(jack_client_t* client,
   fprintf(stderr, "jack_interposer: wrapping process callback\n");
 
   if(!func)
-    func = (int(*)()) dlsym(RTLD_NEXT, "jack_set_process_callback");
+    func = (int(*)(jack_client_t*, JackProcessCallback, void*)) dlsym(RTLD_NEXT, "jack_set_process_callback");
   if(!func)
   {
     fprintf(stderr, "Error dlsym'ing jack_set_process_callback\n");