GPG signature on commit (BB-4445)

gpgsig header appears on changeset page if a commit has GPG signature.

for example: https://bitbucket.org/opentween/opentween-icons/changeset/c08224d30845

this show up as:
{{{
gpgsig ----BEGIN PGP SIGNATURE----
Version: GnuPG v1.4.12 (GNU/Linux)
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=olop
----END PGP SIGNATURE----

first commit
}}}

I would expect the following:

{{

}