scm: refactor scm log encoding test (#1735, #3396, #7597).

Bazaar log depends on locale.
On Japanese Windows, standard out is CP932.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@4961 e93f8b46-1217-0410-a6f0-8f06a7374b81