Move #include <pthread.h> to sanei_thread.h

The sanei header file may need pthread_t.  If it does, make sure it
is available.

include/sane/sanei_thread.h

@@ -61,6 +61,7 @@
 #include "../include/sane/config.h"
 
 #ifdef USE_PTHREAD
+#include <pthread.h>
 typedef pthread_t SANE_Pid;
 #else
 typedef int SANE_Pid;

sanei/sanei_thread.c

@@ -71,9 +71,6 @@
 #if !defined USE_PTHREAD && !defined HAVE_OS2_H && !defined __BEOS__
 # include <sys/wait.h>
 #endif
-#if defined USE_PTHREAD
-# include <pthread.h>
-#endif
 
 #define BACKEND_NAME sanei_thread      /**< name of this module for debugging */