[3381085] Improved way of detecting what version of the documentation to build.
Set the HTML_VERSION environment variable to override the (sensible) default.
First attempt to fix bug [d4e464ae48]: tcl 8.5.15/8.61 breaks python make check on darwin
Fix for [d4e464ae48]: tcl 8.5.15/8.6.1 breaks python make check on darwin
Fix for [d4e464ae48]: tcl 8.5.15/8.6.1 breaks python make check on darwin
Merge trunk. 
Remove obsolete lines in tclOO*Decls.h: TCL_STORAGE_CLASS is not used anywhere in "novem" any more.