tkdiff Code

Primarily to support TclTk 9.0 (and compensate for lost V8.x.x deprecations)
1. Adjust 'requires' syntax to ACCEPT ALL Tcl/Tk 8.5 and BEYOND (incl V9.0)
2. Support BOTH OLD/NEW Tcl V8->V9 tilde semantics transition + Help update(s)
3. newDiff enhanced for typing-validity feedback + new GLOB input syntax support
4. Text search-tool NOW arranges to wrap-around after reporting failed-to-find
5. A latent failure to DELETE Vertical Linearity tags repaired
6. DROPPED specialized CDE visual configuration (now only GTK or default X11)
7. Minor (operationally invisible) Debug enhancements

Update the README to say that the tk8.5 that comes with MacOS will not work, and recommend the version on Homebrew

forgot to bump release to 5.7

chglog updated for release 5.7

Inline instantiation realigned: prevents Heuristic+1 dropouts; broken syntax; better reading

Bookmark annotation prompt now tracks instance AFTER 1st use

Add missing trigger event when recursive inlines are activated

Miscellaneous adjusments:
- Comment out multi-monitor clipping debug msg; only serves to document TK inadequacy
- reword commentary to more accurately reflect recent changes

Remove superfluos checks for tk_version 8.5

For MacOS, don't override the color options if Tk >=8.6, since it now handles the OS dark/light theming correctly.

Fix a trucated label in the preferences window by doing font measure

Miscellaneous fixes:
- Popup menu activation permitted when over L/R scrollbars
- Somewhat useless Dbg message for FAILED edge-clipping .vs. multi-monitor conditions
Basically documents intractability of problem - inadequate TK information available.
- Initialization to avoid situational 'missing variable' error for highly unlikely
mouse position during startup position when positioned over a Tooltip location.