readTipsyArray() can hammer a file system with unnecessary file opens

[trquinn]

TreePiece::readTipsyArray() is called as a broadcast to all TreePieces, but all TreePieces don't need to read data. In particular, there is an optimization such that only one TreePiece per processor loading data (see TreePiece::loadTipsy()). Hence there can be excessive file opens when loading array data, such as when we restart from an output. This may lead to odd file system failures such as "Cannot send after transport endpoint shutdown".

[trquinn]

TreePiece::readFloatBinary() can also have this problem.

[trquinn]

Attempting to optimize TreePiece::readTipsyArray() did not fix the file system problem. It will likely need a way to reduce the number of reading processors.