cmdlinelib.c now calls system() rather than doing its own tokenisation

(which was extremely heavy on calls to malloc()).

Moved include/command.h to include/gpxe/command.h, since it's
gPXE-specific.

src/include/command.h

@@ -1,15 +0,0 @@
-#ifndef COMMAND_H
-#define COMMAND_H
-
-#include <gpxe/tables.h>
-
-struct command {
-	const char *name;	 	     				// The name of the command
-	const char *usage;						// Description of how to use the command
-	const char *desc;						// Short description of the command
-	int ( *exec ) ( int argc, char **argv);				// The command function to call
-};
-
-#define __command __table ( commands, 01 )
-#endif
-