Fix error when editing a DWG file

Steps to reproduce:

1. create 2 non administrator users
2. create a Folder and share it with the two above users with Write permission
3. drop a DWG file in this folder
4. Synchronize the newly created folder with Drive for each user
5. On 2 different PCs (Windows 10), add a Drive account which corresponds to each user
6. With one account, open the DWG file with Autocad and make repeated changes

At one moment, you will observe:

• creation of a .bak file => normal but maybe it should be ignored by Drive synchronization
• creation of a .tmp file => normal? but it should be ignored by Drive synchronization
• Conflict error on the second PC where no modification of the DWG file is done => this is the main issue (please see attach screenshot)

Please find attach the report from both Drive clients:

• report_170628_145204.zip on the PC where no modification is done
• report_170628_145342.zip on the PC where the modifications are done