CLK_TCK backwards compatibility revisit

[DavidGriffith]

The file xv-20091215-werner-fink-multiple-fixes.patch.mime addressed, among other things, switching away from using CLK_TCK to sysconf(_SC_CLK_TCK).

The patch number four uses the correct tick definition of the system instead of a hard defined value. In fact CLK_TCK isn't defined anymore on newer Linux systems as it now becomes variable at boot time.

Later on, I want to have the Makefile (or Autoconf) check to see if we should use sysconf(_SC_CLK_TCK) and if not, use the constant CLK_TCK.