Added comments raising questions about possible updates to channel
drivers on Windows.
Implementation of [b42b208ba4]: file attributes -readonly on Cygwin. For completeness, implemented -archive, -hidden and -system as well.
Only write back file attributes if any of them really changed.
Implement RFE [b42b208ba4]: file attributes -readonly (and -archive, -hidden, -system) on Cygwin.
New test iortrans-4.8.1 exposes segfault bug [721ec69271].
Test iogt-2.4 is another segfault demo for [721ec69271].
Test iogt-2.4 is another segfault demo for [721ec69271].
Test iocmd-23.11 demos another segfault.
Test iocmd-23.11 demos another segfault.
Minimal patch to fix iocmd-23.11.  Might not be the best fix, but is *a* fix.
Merge minimal fix for iocmd-23.11.
Note that top channel regeneration is removed, so that Preserve/Release
call pairs are sure to operate on the same pointers.  Other bug fixes
may need to change that.
Cherry-pick [c54059aaad] from trunk: Added support for reporting TEA-like info via pkg-config. 
Add missing @TCL_LIB_FLAG@ (derived from ticket [5bcb5026ad])
Add missing @TCL_LIB_FLAG@ to tcl.pc.in (derived from ticket [5bcb5026ad])
merge trunk