Global Download Method setting changing from public to private automatically

Issue Summary

Since Download Method variable "file_download" is a global variable stored in the database, if two users simultaneously upload the file as private files, following scenario can happen:

If initial value of file_download is "Public"

Step A1 File A: get the original value of file_download (i.e. Public)
Step A2 File A: Set file_download to Private
Step B1 File B: get the original value of file_download. This would be “private” because file_download is a global variable and in “Step A2” it has been set to Private.
Step A3 File A: Generate the path for file A
Step A4 File A: Set back file_download to original value as in step A1 (this would set file_download to Public)
Step B2 File B: Set file_download to Private
Step B3 File B: Generate the path for File B
Step B4 File B: Set back file_download to original value as in step B1 (this would set file_download to Private)

The outcome of above scenario will be that the global download setting would be now “Private” and CSS compression would get disabled (because for css compression the Download Method should be Public) causing the page to break in IE (in case there are more than 32 css on the page).