ENH: stream adjustments

• make stream constructors explicit

• remove "using std::ifstream", "using std::iofstream" statements for a cleaner namespace.

• copy/move assignments for ITstream

• IStringStream: default construct and construct from std::string instead of Foam::string

• reduce some overhead in masterOFstream

• simplify Pstream handling of string variants (#1525)

added 1 commit

• 0ff02713 - ENH: stream adjustments

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mentioned in commit 0a9295b2

merged