Define PROG, for newer versions of skalibs

Needed to build from our source tarball on some Gentoo systems.

Closes #239.
Closes #254.

src/examples/termemu.cc

@@ -52,6 +52,11 @@
 #include "locale_utils.h"
 #include "sigfd.h"
 
+/* For newer skalibs */
+extern "C" {
+  const char *PROG = "termemu";
+}
+
 const size_t buf_size = 16384;
 
 void emulate_terminal( int fd );