QDomDocument::save() is slow when saving to a network drive

The performance of QDomDocument::save() is very slow when saving to a network drive. This is a regression from Qt 4.3.

Preparation:
Assign a UNC path to a network drive, e.g, \\otherpc\share to Z:\

Steps to reproduce:

1) Build the attached example.
2) Execute the example with a local path.as an argument e.g,

> sample.exe C:\Qt\outputtest

3) Execute the example with a network drive path as an argument argument, e.g,

> sample.exe Z:\outputtest

This has been tested against both Qt 4.7.1 and 4.3.5 with the following result:

4.7.1 Local 1731 ms
4.7.1 Network 30232 ms
4.3.5 Local 1778 ms
4.3.5 Network 1841 ms