reading in covariate file

    cfile   file containing the fixed effects as NxP matrix
            (N=number of samples, P=number of covariates)

def readCovariatesFile(fFile):
    """"
    reading in covariate file

    cfile   file containing the fixed effects as NxP matrix
            (N=number of samples, P=number of covariates)
    """
    assert os.path.exists(fFile), '%s is missing.'%fFile
    F = SP.loadtxt(fFile)
    if F.ndim==1: F=F[:,SP.newaxis]
    return F