71x cmsShow script: fix warning about missing version.txt

[alja]

FROM_RELEASE variable was not initalised which caused false warning.

[cmsbuild]

A new Pull Request was created by @alja (Alja Mrak-Tadel) for CMSSW_7_1_X.

71x cmsShow script: fix warning about missing version.txt

It involves the following packages:

Fireworks/Core

@Dr15Jones, @cmsbuild, @alja, @nclopezo, @Degano, @ktf can you please review it and eventually sign? Thanks.
You can sign-off by replying to this message having '+1' in the first line of your reply.
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@nclopezo, @ktf you are the release manager for this.
You can merge this pull request by typing 'merge' in the first line of your comment.

[ktf]

@alja remember to sign off..