allow "~" to be present in a tag name

[Michal Novotny <clime@redhat.com>]

Hello,

currently, if I try to create a tag that has tilde "~"  in name, an
error is raised. E.g.

$ git tag rpkg-util-1.4~rc1
fatal: 'rpkg-util-1.4~rc1' is not a valid tag name.

Now, actually it would be very cool if tilde was allowed in a tag name
because we would like to use it for tagging pre-releases of (not-only
rpm) packages.

Is there some deep technical reason why tilde cannot be present in a
tag name? I tried that e.g.

git tag rpkg-util-1.4%rc1

but percentage sign does not seem to be particular fitting for
pre-release marking.

Thank you
clime