[http] Improve upload file api.

If query string "ret-json=1" is added to the file upload link,
the API will return a json format result. The format of the
result is:
[{'name': 'file1', 'id': 'id1'}, {'name': 'file2', 'id': 'id2'}]

If file with the same name exists, the uploaded file will be renamed.
In such cases, the new name will be included in the json.
[scripts] added a script for mysql database upgrade
update version to 2.0.8
fixed database upgrade scripts for python2.6
fixed database upgrade scripts
fixed database update scripts

The content of seafile.conf in old seafile servers stills contains the "database"
section even if the database is sqlite3.
removed duplicate definitions
Merge pull request #499 from DATAWERK/fix_build_error

removed duplicate definitions
[client] Use single worker thread in getfs proc.
[server] Fix a error handling bug in get_last_modified().
[server] Add 0644 to file mode when upload/update from web.
Don't download history commit and fs objects.