- markup fix

- explain Python/ceval.c from what; lots of people don't use a source
  distro any more

Doc/lib/libsys.tex

@@ -479,9 +479,9 @@ else:
   Activate dumping of VM measurements using the Pentium timestamp
   counter, if \var{on_flag} is true. Deactivate these dumps if
   \var{on_flag} is off. The function is available only if Python
-  was compiled with \code{--with-tsc}. To understand the output
-  of this dump, read \code{Python/ceval.c}.
-
+  was compiled with \longprogramopt{with-tsc}. To understand the
+  output of this dump, read \file{Python/ceval.c} in the Python
+  sources.
   \versionadded{2.4}
 \end{funcdesc}