Support TAB variable

ppremake/configure.in

@@ -1,6 +1,6 @@
 dnl Process this file with autoconf to produce a configure script.
 AC_INIT(ppremake.cxx)
-AM_INIT_AUTOMAKE(ppremake, 0.61)
+AM_INIT_AUTOMAKE(ppremake, 1.00)
 AM_CONFIG_HEADER(config.h)
 
 AC_PREFIX_DEFAULT(/usr/local/panda)

ppremake/ppremake.cxx

@@ -298,6 +298,11 @@ main(int argc, char *argv[]) {
     global_scope.define_variable("PPREMAKE_CONFIG", ppremake_config);
   }
 
+  // Also, it's convenient to have a way to represent the literal tab
+  // character, without actually putting a literal tab character in
+  // the source file.
+  global_scope.define_variable("TAB", "\t");
+
   PPMain ppmain(&global_scope);
   if (!ppmain.read_source(".")) {
     exit(1);