TclTk update to 8.6.13 fixing large integer bug

[dhomeier]

Fixes a number of test failures like #956 (comment) and by way of this also the test_tcl failures in our Python builds.

Checking the changes made though the last upstream update, all library versions that have changed are again just the non-public ones like

		!%p/lib/itcl4.2.3/libitcl4.2.3.dylib
		!%p/lib/sqlite3.40.0/libsqlite3.40.0.dylib

so this should be OK to update without packaging as a new version?

[dmacks]

blocking on #923 (can tcltk remain using ppkg-config, so we don't need to wait for pkgconf to land?)

There's a comment adjacent to the Version:
# update itcl path-flags in "itk" and versions in "iwidgets" when updating
that does not seem to have been followed.