extensions: move wrapfilecache function from fsmonitor It makes more sense to put this in core, so other extensions can trivially get access to it without having to rely on importing fsmonitor.

chmod: create a new file when flags are set on a hardlinked file For performance reasons we have several repositories where the files in the working directory of 1 repo are hardlinks to the files of the other repo When an update in one repo results in a chmod of a such a file, the hardlink has to be deleted and replaced by a regular file to make sure that the change does not happen in the other repo