Add missing std:: qualifiers and missing includes of iostream.

This pull request adds missing std:: qualifiers and missing includes of iostream that are necessary to compile CMSSW against ROOT6.  It does nothing else.  These changes are *not* ROOT6 specific, and can be merged into
the main 7_0_X line.  I tested with checkdeps -a and rootMatrix.py -s and everything passes.

Signatures should be bypassed.
Retesting is at your discretion.
I am also running the full rootMatrix.py, which is still in progress.