Port back from ROOT6 IB for commonality (L1)

[wmtan]

This PR ports back simple changes made in CMSSW_7_4_ROOT6_X in the L1 L2 category that are desirable or harmless for CMSSW_7_4_X, in order to increase code commonality. All affected files will be identical in the two releases after this PR is merged. Changes were successfully tested with the short relval matrix.
The changes are:
1)enum declarations needed for ROOT6.
2) removal of an unneeded link dependency
3) Addition of a missing include

[cmsbuild]

A new Pull Request was created by @wmtan for CMSSW_7_4_X.

Port back from ROOT6 IB for commonality (L1)

It involves the following packages:

CondFormats/L1TObjects
DataFormats/L1GlobalMuonTrigger
L1Trigger/GlobalTrigger

@diguida, @cerminar, @cmsbuild, @nclopezo, @ggovi, @mmusich, @mulhearn can you please review it and eventually sign? Thanks.
@Martin-Grunewald, @apfeiffer1 this is something you requested to watch as well.
You can sign-off by replying to this message having '+1' in the first line of your reply.
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If you are a L2 or a release manager you can ask for tests by saying 'please test' in the first line of a comment.
@Degano you are the release manager for this.
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[diguida]

please test