sdx.kit/main.tcl needs update for package vcompare

&| Failure...

Because the package command doesn't understand alpha and beta version numbers (yet, see TIP#268), I've repaired my SDX (main.tcl, line 6) so that I can source it properly:

  package require starkit

   # old tclkits have broken "sourced" symlink detection (in their "starkit" pkg)
   # let SDX work in older ones but don't allow sourcing, which is a new feature
   if {[starkit::startup] eq "sourced" &&
      [package vcompare [lindex 0 [split [info patchlevel] ab]] 8.4.9 >= 0} return

  package require app-sdx

This fixes this particular comparison to work properly even with the broken package command. (Hence, even old tclkits will work when sourcing SDX.)

Thank you for this amazing utility! :-)