CLOSESOCKETFUNCTION: added

Introduced the initial setup to allow closesocket callbacks by making
sure sclose() is only ever called from one place in the libcurl source
and still run all test cases fine.

lib/setup_once.h

@@ -240,7 +240,6 @@ struct timeval {
 #  define sclose(x)  close((x))
 #endif
 
-
 /*
  * Uppercase macro versions of ANSI/ISO is*() functions/macros which
  * avoid negative number inputs with argument byte codes > 127.