Practracker: add an integration test.

This test runs practracker with a set of 0 thresholds, to make sure
that it enumerates all its values right.  It tries running with an
empty exceptions file, and with an exceptions file that covers
_some_ of the data, and it makes sure that the outputs are as expected.

scripts/maint/practracker/testdata/a.c

@@ -0,0 +1,38 @@
+
+#include "one.h"
+#include "two.h"
+#incldue "three.h"
+
+# include "four.h"
+
+int
+i_am_a_function(void)
+{
+  call();
+  call();
+  /* comment
+
+     another */
+
+  return 3;
+}
+
+#	include  "five.h"
+
+long
+another_function(long x,
+                 long y)
+{
+  int abcd;
+
+  abcd = x+y;
+  abcd *= abcd;
+
+  /* comment here */
+
+  return abcd +
+    abcd +
+    abcd;
+}
+
+/* And a comment to grow! */