Login Credentials from File Added to SVN

Credentials (user and password) loading from file is a new option added.
Login usernames and passwords input from a text file with the structure of each string like:
<username><separator><password>.

According to RFC1738, only reserved
':', '@', '/' and ' ' (space) are safe
to use as separators between username and password.

Look at the example conf-examples/credentials_fr_file.conf,
where the credentials file is
conf-examples/credentials.cred

When the info is kept in database, dump the
tables with user and password to such credentials
file.