and some niceness in derivative

Not if this ever happens anyway. So more accurate averaging procedure.

on RHEL-6

The solution (setting bin width to 1.0) is admittedly arbitrary, but in
lack of more information it seems to be the only solution (apart from
throwing an exception).

Add rigorous tests for it as well.

And use a standard algorithm instead of home-brewing it.

Signed-off-by: Karl Palmen <karl.palmen@stfc.ac.uk>

Includes basis for creating a simulation workspace, the fitting function itself and the TobyFit
resolution model.

Since VectorHelper::rebin() requires current X vector with
one more entry than the current Y vector, even if the
Workspace2D is a distribution, we need to adjust the current
X vector before calling rebin.  This is a convenience method
that essentially reverses the convertToBinCentre() method, so
it seems to belong in VectorHelper.
refs #5285

Fixes #3351: test for VectorHelper and some refinement of that method to split a comma-delimited string. Refs #3349: BoxController XML serialize/deserialize.

Flatbackground now works for non-distribution data and SANS Display Mask is now clearer re #2612 fixes #2599