Allowed to check gradients with non-contiguous inputs.

When the input is not contiguous,
the checkGradients() was reporting a wrong numerical gradient.

You can reproduce the problem by:

    require 'totem'
    require 'nn'

    local tester = totem.Tester()
    local test = {}
    function test.test_nonContinous()
        totem.nn.checkGradients(tester, nn.Sigmoid(), torch.randn(3, 5):t())
    end

    tester:add(test):run()