#638 [tcl_findLibrary] armor against relative pathnames?

[Don Porter]

When testing Tk 8.5.13 for release, we ran into troubles
when a realtive pathname value in TK_LIBRARY caused
a failure to find tk.tcl after a change of the working directory.
Using relative pathnames there is a bad idea, but in case it
happens, perhaps [tcl_findLibrary] ought to be normalizing
it's pathnames (or otherwise preventing relative pathnames)
as it puts them on the search path?