Fix compiler warning for QIEXXDataFrames (Backport of #8206)

[agude]

This fixes the compiler warnings introduced in #8103 (see #8103 (comment)) and is a backport of #8206.

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_4_X.

Fix compiler warning for QIEXXDataFrames (Backport of #8206)

It involves the following packages:

DataFormats/HcalDigi

@cmsbuild, @civanch, @nclopezo, @mdhildreth can you please review it and eventually sign? Thanks.
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[davidlange6]

@agude - thanks - is there a 73x version coming as well? Would be good to be able to include in the next 73x release.

[agude]

Hi @davidlange6,

Since the 7_3 PR (#8013) hasn't been merged yet, I just pushed an update there instead of opening a whole new PR: #8013 (comment)

[slava77]

@cmsbuild please test

[cmsbuild]

The tests are being triggered in jenkins.

[cmsbuild]

+1
Tested at: 5c27ab4
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-8207/6613/summary.html