Use setUp/tearDown() for NumFormatter test case locale setup.

Use setUp/tearDown() for NumFormatter test case locale setup.

Setting the locale in the ctor of the test object doesn't work because the
locale is changed by the other tests that run before this one, use the
initialization method provided by cppunit to change the locale instead, this
is somewhat wasteful but at least it does work, unlike the old version.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66718 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775