Add an option to force the use of PollingDirectoryWatcherStrategy
Should work on any platform
(Not Linux only)
See previous PR on this topic :
https://github.com/pocoproject/poco/pull/2881
On Linux, inotfy does not work for network volumes (such as NFS).
See https://stackoverflow.com/questions/4231243/inotify-with-nfs
By adding flag POCO_DW_FORCE_POLLING in Foundation/Config.h,
the use of PollingDirectoryWatcherStrategy is forced.
This is not the same behavior as flag POCO_NO_INOTIFY.
This only disables compilation of DirectoryWatcher.
b651764007