Applied patch by Andreas Leitgeb so that [string cat]'s compiled bytecode optimally groups args by 255 for INSTR_STR_CONCAT1.
Backing out commit [cddbfc3081], fix for bug [82521bfb6734f891dd]

The "optimisation" in that commit assumes that the last byte in the
generated bytecodes is an INST_TRY_CONVERT if it equals 64. This is an
invalid assumption, it could be 64 and not be an instruction.
[bc5b790099] Improper calculation of new dstLimit value.  New test io-12.7.
[bc5b790099] Improper calculation of new dstLimit value. New test io-12.7.
[bc1a96407a] Partial solution should avoid crash, but may lead to wrong behavior.
Possible fix for testing.
test cases
fix [bc1a96407a]
Fix [59a2e78e54d3361c33b8cd6eef55d384d8abecd7|59a2e78e54] : tclWinTime.c does not compile with MSVC14. 
Eliminate use of __MINGW32__ macro everywhare, as it is deprecated.
Fix [59a2e78e54d3361c33b8cd6eef55d384d8abecd7|59a2e78e54] : tclWinTime.c does not compile with MSVC14. 
Eliminate use of __MINGW32__ macro everywhare, as it is deprecated.
[2039178] Remove false claims about TCL_INTERP_DESTROYED flag bit in command traces.
[2039178] Remove false claims about TCL_INTERP_DESTROYED flag bit in command traces.
New test io-53.15 for [ed29c4da21].
New test io-53.15 for [ed29c4da21].
[ed29c4da21] Don't let BLOCKED state get converted into a channel error.
[ed29c4da21] Merge patch from 8.5, still not a complete fix.
Another test so both DoRead and MBRead are covered.
Add Colin's test for coro floor above street level [Bug #3008307]
[ed29c4da21] Completed fix for [chan copy] handling [chan blocked].
[bf7135428c] Restore the Tcl_Write() return value logic.