WatchChanges defaults to include sub directories

[mastoj]

When watching files FAKE will look up the folder of each file and watch that folder including the subdirectories. This is a bad default since it can potentially lead to watching to many files and thus failing the build. Happened me in a quite small repo, but for some reason I reach the limit since also the .git folders packages and others were watched.

Two alternative solutions.

1. Not include subdirectories
2. New overload where one can specify the behavior.

I think number 2 is best since other might be dependent on the feature as is.

[dsyme]

fixed already