.min of FRDRV does not work properly

[pelegm]

For example,

In [1]: import drv.real

In [2]: ps = [0, 1, 2, 3, 5, 0, 13, 21, 34, 0]

In [3]: fp = drv.pspace.FDPSpace(ps)

In [4]: fr = drv.real.FRDRV('fr', fp, lambda x: x ** 2 + 7)

In [5]: fr.min
Out[5]: 7

In [6]: fr.xs
Out[6]: [7, 8, 11, 16, 23, 32, 43, 56, 71, 88]

In [7]: fr.ps
Out[7]: 
[0.0,
 0.012658227848101266,
 0.02531645569620253,
 0.0379746835443038,
 0.06329113924050633,
 0.0,
 0.16455696202531644,
 0.26582278481012656,
 0.43037974683544306,
 0.0]

Related: #6.