Fix crash of Folder as Workspace when too many directory changes happen:
Remove limit for amount of queued directory changes: use auto-reset Event instead of Semaphore.
Fix#6005, fix#5907, fix#3740, close#6005
Closes#2061
To reproduce such bug, the file foo.txt to monitor should be in the root folder (ie. c:\foo.txt).
The algorithm is check if folder path has '\' at the end, if no, then add a '\' then append file name.
In the original code, instead of checking folder path, the file name is checked. Since file name doesn't contain '\' (ie. c:\temp), a '\' is always added on folder path which has no '\' at the end. it works for none root folder such as C:\, E:\ or F:\.
