If a project is checked out from SVN, we can use the value of $SVN_REVISION to
identify which revision the artifact corresponds to.

I suggest the following environment variables be created for projects cloned via
Mercurial:

1) HG_CHANGESET
Example value: '95:b66be5e651e0'
How to get it: parse the output of 'hg id --id --num .'

2) HG_BRANCH
Example value: 'default'
How to get it: 'hg id --branch .'

2) HG_TAGS
Example value: 'tip tag1 tag2'
How to get it: 'hg id --tags .'

3) HG_CHANGESET_FULL
Example value: 'b66be5e651e0207c05f2ed08e3a68f6309e5a547'
How to get it: 'hg id --id --debug .'