[PATCH 0 of 3] series of patches to improve Mercurial performance on case folding systems - minor cleanups

[Petr Kodl]

Minor cleanup of the patchset.

The win32 specific test code from last patch has been moved to util.py
as the coding practices suggest and isolated into separate function.

- first patch is fix for performance regression reported in 1286

- second patch eliminates calling normath when not needed - more details in the patch header

- the last patch tries to balance directory level stat with file level stat calls
when it makes sense