BF: A few more places in which the fe.life struct appears.

Here are a few more places where the `fe.life` struct makes an appearance. 

Note that I still can't run `life_test` on master, and this PR does not solve that. I am currently getting the following error on master: 

<pre><code>
Inner matrix dimensions must agree.

Error in feGet (line 965)
    val = feGet(fe,'Mfiber')*feGet(fe,'fiber weights');


Error in feGet (line 1293)
    val     = reshape(feGet(fe,'pSig fiber'), nBvecs, nVoxels);


Error in feGet (line 1403)
    predicted = feGet(fe,'pSig f vox');


Error in life_test (line 29)
rmse   = feGet(fe,'vox rmse');
 
</code></pre>