TCL, get version (8.4, 8.6 or latest one)

Under tclsh
# tclsh
% puts $tcl_version
% 8.4

Version include build info.
# tclsh
% puts $tcl_patchLevel
% 8.5.18

Under DOS
# echo "puts $tcl_version;exit 0" | tclsh
invalid command name "puts 8.4; exit 0"