Added 'system.api_version', which will be incremented every time the API changes. (sans brainfarts)

configure.ac

@@ -1,5 +1,7 @@
 AC_INIT(rtorrent, 0.9.1, jaris@ifi.uio.no)
 
+AC_DEFINE(API_VERSION, 1, api version)
+
 AM_INIT_AUTOMAKE
 AM_CONFIG_HEADER(config.h)
 AM_PATH_CPPUNIT(1.9.6)

src/command_local.cc

@@ -328,6 +328,7 @@ initialize_command_local() {
   CMD2_ANY         ("system.hostname", std::bind(&system_hostname));
   CMD2_ANY         ("system.pid",      std::bind(&getpid));
 
+  CMD2_VAR_C_STRING("system.api_version",           (int64_t)API_VERSION);
   CMD2_VAR_C_STRING("system.client_version",        PACKAGE_VERSION);
   CMD2_VAR_C_STRING("system.library_version",       torrent::version());
   CMD2_VAR_VALUE   ("system.file.allocate",         0);