See the previous commit for why. Marked as API change since osutil.listdir()
seems widely used in third-party extensions.
The win32mbcs extension is updated to wrap both util. and windows. aliases.
Thoughout hg code, we see a pattern of attempting to remove a file and then
catching and ignoring any errors due to a missing file in the calling code.
Let's unify this pattern in a single implementation in the vfs layer.
The 'scmutil' is growing large (1500+ lines) and 2/5 of it is related to vfs.
We extract the 'vfs' related code in its own module get both module back to a
better scale and clearer contents.
We keep all the references available in 'scmutil' for now as many reference
needs to be updated.
