BF: deal with random signs for PCA on Windows
BF: deal with random signs for PCA on Windows

Windows seems to give random signs for the PCA even across runs on the
same data; make sure tests don't fail because of this.

alexis-roche/nipy,nipy/nireg,arokem/nipy,alexis-roche/nireg,alexis-roche/nipy,alexis-roche/register,alexis-roche/nireg,alexis-roche/register,alexis-roche/nipy,arokem/nipy,nipy/nireg,alexis-roche/nipy,alexis-roche/niseg,alexis-roche/register,arokem/nipy,arokem/nipy,alexis-roche/niseg