Modification to Autoconf to prefer tcl8.6+ or tcl9 over tcl8.5 (or older)

This allows build scripts that depend on new function in 8.6 to know
that the best native tclsh was detected and used by ./configure
Merging with trunk
Regenerate configure with autoconf-2.13.  Mostly repairs line numbers.
Updating with latest fixes from trunk
[Bug 3608360]: Test to make sure we never let [file exists] do globbing.
[Bug 3608360]: Test to make sure we never let [file exists] do globbing.
[Bug 3608360]: Test to make sure we never let [file exists] do globbing.
Test independence in unixFCmd.test.
Test independence in unixFCmd.test
Test independence in fileSystem.test
Test independence in fileSystem.test
[Bug 3606387]: Fix isolation of test scan-7.4.
Also updated scan.test to use tcltest 2 properly.
[Bug 3606387]: Fix isolation of test scan-7.4.
[Bug 3606390]: Fix isolation of test string-6.37.
[Bug 3606390]: Fix isolation of test string-6.37.
Back out bug fix for [Bug 2893771], because it was the cause of the regression.
[Bug 2893771]: file stat fails on locked files on win32.
Test independence in fCmd.test.
Test independence in fCmd.test
make sure that [file stat] returns the right data, even for locked files.