Remove "cosmetic" (?) thresholding line from chebfun.roots().

This closes #1200.  With this line in place, we can get bizarre things
like the following:

  >> f = 1e18*chebfun(@(x) x - 1.5e4, [1e4 2e4])
  f =
     chebfun column (1 smooth piece)
         interval       length   endpoint values
  [   1e+04,   2e+04]        2    -5e+21    5e+21
  Epslevel = 1.238223e-15.  Vscale = 5.000000e+21.
  >> roots(f)
  ans =
       0

Note that the point 0 isn't even in the domain of this chebfun!

An alternative to removing this line like we do here would be to
eliminate the dependence of the threshold on vscale.
This fix loosens the tolerance (htol) used in roots@chebfun for determining if a root is spurious when it is close to another root. The current tolerance is a bit of too tight, causing a few failures in tests for min, minandmax, etc when 1st-kind points are used. By loosening the current tolerance which was introduced by commit b704d284 by a factor of 10, the failures or crashes related to this are gone.
Merge remote-tracking branch 'origin/fix-chebfun-roots-thresh' into development
Merge remote-tracking branch 'origin/fix-roots' into development