bug#51609: version.texi UPDATED field does not account for timezone; can cause unnecessary documentation rebuilds, which could fail

[Ryan Schmidt]

The method by which automake decides to regenerate version.texi and thereby to 
regenerate texinfo-based documentation is flawed because it does not account 
for the fact that the user's timezone may be different from the developer's 
timezone. The version.texi UPDATED and UPDATED-MONTH fields do not specify a 
timezone. If configure has been modified and if the user's timezone is 
sufficiently different from the developer's, then UPDATED or less frequently 
UPDATED-MONTH may change even though the texinfo sources' timestamps have not, 
which will cause an unnecessary documentation rebuild, which may fail. For a 
build failure that was caused by this flaw, see:

https://trac.macports.org/ticket/63570#comment:5