Add sys_exec () and libprocess wrapper, fix ramdisk tar parsing

libprocess/process.c

@@ -17,3 +17,5 @@ int process_spawn (process_func_t func, void* argument_ptr) {
 int process_quit (void) { return quit (); }
 
 void* process_argument (void) { return argument_ptr (); }
+
+int process_exec (const char* path) { return exec (path); }