tests: Added numerous tests.

The tests are taken almost verbatim from the open source project PicoC. It can
be found at https://code.google.com/p/picoc/.

The tests range from very simple/trivial ones to more complicated. My view is
that the more tests the better. Without tests like this I was very reluctant to
make any changes to tcc for the fear of breaking things.

The tests pass on Win32, OSX, Linux x86 and x86_64. One or two tests fail on
each platform due to differences in the runtime library.

tests2/16_nesting.c

@@ -0,0 +1,21 @@
+#include <stdio.h>
+
+int main()
+{
+   int x, y, z;
+
+   for (x = 0; x < 2; x++)
+   {
+      for (y = 0; y < 3; y++)
+      {
+         for (z = 0; z < 3; z++)
+         {
+            printf("%d %d %d\n", x, y, z);
+         }
+      }
+   }
+
+   return 0;
+}
+
+/* vim: set expandtab ts=4 sw=3 sts=3 tw=80 :*/