cpan-base: add perl version to PR

cpan-base: add perl version to PR

Makes perl modules rebuild on perl version change, since binary compatibility
could be broken with that (although perl itself tries to maintain it  within
patchlevel range, like 5.8.7 -> 5.8.8).

This is conditional on PACKAGE_ARCH, since there is nothing to rebuild for
pure perl modules (and those should use 'PACKAGE_ARCH = "all"') even if they
break with perl version change.

This also should ease transition to perl 5.10.1.

Signed-off-by: Roman I Khimov <khimov@altell.ru>