Consistently use ‘our’ instead of ‘use vars’.

Consistently use ‘our’ instead of ‘use vars’.

At file scope of a file containing at most one ‘package’ declaration,
‘use vars’ is exactly equivalent to ‘our’, and the latter is preferred
starting with Perl 5.6.0, which happens to be the oldest version we
support.

(This change has nothing to do with the previous two, but I want to make the
same change in Autoconf and that means doing it here for all the files synced
from Automake.)

(I don’t know why, but this change exposed a latent bug in FileUtils.pm where
the last pod block in the file didn’t have a ‘=cut’ delimiter, so the code
after it was considered documentation, causing ‘require FileUtils’ to fail.)

* lib/Automake/ChannelDefs.pm
* lib/Automake/Channels.pm
* lib/Automake/Condition.pm
* lib/Automake/Configure_ac.pm
* lib/Automake/DisjConditions.pm
* lib/Automake/FileUtils.pm
* lib/Automake/General.pm
* lib/Automake/Getopt.pm
* lib/Automake/Options.pm
* lib/Automake/Rule.pm
* lib/Automake/RuleDef.pm
* lib/Automake/VarDef.pm
* lib/Automake/Variable.pm
* lib/Automake/Wrap.pm
* lib/Automake/XFile.pm:
  Replace all uses of ‘use vars’ with ‘our’.

* lib/Automake/FileUtils.pm:
  Add missing ‘=cut’ to a pod block near the end of the file.