Backport various improvements from Tcl 8.5
merge-mark
Add some extra paths on Windows for finding tclConfig.sh, for mSys and Cygwin shell.
Add some extra paths on Windows for finding tclConfig.sh, for mSys and Cygwin shell. 
Improve some comments and quoting, no change in functionality.
Add some extra paths on Windows for finding tclConfig.sh, for mSys and Cygwin shell.
Improve some comments and quoting, no change in functionality.