Feature/fudgeShift

[jsampaio]

A cleaned-up version of pull request #221.

This change introduces a new mode for the shift the problem window. In this new mode, the values of m in the introduced cells are copied from the cells at the border, instead of the values of ShiftMagL/R (current mode). This new mode is activated by setting FudgeShift = true (false by default).

When using auto-shifting procedures (e.g. ext_centerWall), it is still necessary to set the parameters ShiftMagL/R because they're used to determine the shift direction (as is the previous behaviour).

Modifications:

• In engine/shift.go: Added the user-accessible flag ‘FudgeShift’ to activate this shift mode. Modified engine.Shift.
• In the (cuda) implementation of the shift: new functions: cuda.ShiftFudgeX, cuda.ShiftFudgeY (and related .cu).
• added test/fudgeShift.mx3 to test to check if it behaves as announced.