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

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

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.

In one place ‘our’ was not actually necessary and was switched to ‘my’.

(This change has already been made in Automake and applied to the
shared Perl code via the previous ‘make fetch’ commit.)

* lib/Autom4te/C4che.pm
* lib/Autom4te/ChannelDefs.pm
* lib/Autom4te/General.pm: Replace all uses of ‘use vars’ with ‘our’.
* bin/autoheader.in: Replace all uses of ‘use vars’ with ‘our’.
  Remove an unnecessary ‘local’.
* bin/autoscan.in: Convert ‘use vars’ variables to ‘my’ variables.