I just went through all of the externals that include t_tk.h and found that none of them actually need to include it, since none of them actually use the functions or macros declared in t_tk.h. Since pd- devel has removed t_tk.h, and hopefully pd-vanilla will soon also ditch t_tk.h, I have removed #include "t_tk.h" from everywhere it was doing nothing (but preventing pd-devel-extended from compiling).
I hope this is ok with everyone. I couldn't see any reason to keep a header that was unused.
.hc
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All mankind is of one author, and is one volume; when one man dies, one chapter is not torn out of the book, but translated into a better language; and every chapter must be so translated.... -John Donne