Fix compiler warning for QIEXXDataFrames

[agude]

This fixes the compiler warnings introduced in #7950 (see #8103 (comment)).

Additionally we have done the following:

• Replace "magic numbers" with constants (see Update HCAL Packing/Unpacking #7950 (comment))
• Add "flag" word which will inevitably be required operationally

[cmsbuild]

A new Pull Request was created by @agude (Alexander Gude) for CMSSW_7_5_X.

Fix compiler warning for QIEXXDataFrames

It involves the following packages:

DataFormats/HcalDigi

@cmsbuild, @civanch, @nclopezo, @mdhildreth can you please review it and eventually sign? Thanks.
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[slava77]

@cmsbuild please test

[cmsbuild]

The tests are being triggered in jenkins.

[cmsbuild]

+1
Tested at: 3c8977b
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-8206/221/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-8206/221/summary.html