Enhance the way path checking is done in ParquetFileWriter.mergeFooters

To ensure a metadata summary is only written to the same path as the files from which the summary is created, there is a check against the the root path for each footer's file. Only the path is compared, which leaves a possibility that the same path on 2 different types of filesystems (hdfs vs. file for example) could cause some unexpected or erroneous output.

This outcome would be unlikely, but it is not explicitly prevented anywhere which exposes risk to future changes.

Reporter: Chris Albright

_{Note: This issue was originally created as PARQUET-125. Please see the migration documentation for further details.}

首先定位 ParquetFileWriter.mergeFooters，并检查每个 footer 的文件路径如何与根路径进行比较。确认比较不仅包含路径，还包含文件系统类型，并验证 summaries 不能合并来自不同文件系统实现的文件。