git svn will cache svn credential by default.

[mazong1123]

This is not good. No way to remove the cache unless delete the file at ~/.subversion/auth/svn.simple for Linux or %HOMEPATH%\.subversion\auth\svn.simple for Windows.

We should always append --no-auth-cache to prevent the cache.

[mazong1123]

Has to temporarily rename the credential cache files and recover them after main process finished.