Algorithm's default ProcessGroups does not work with 2 inputs

[mantid-builder]

Original Reporter: @jzikovsky

Original Owner: @jzikovsky

Refs http://trac.mantidproject.org/mantid/ticket/996, http://trac.mantidproject.org/mantid/ticket/812

If your algorithm does NOT inherit from PairedGroupAlgorithm, and gets these inputs:

Input1 : groupA
Input2 : groupB

It is processed like this:

Input1 : A1
Input2 : A1

then

Input1 : A2
Input2 : A2

For example, try IntegratePeaksMD with two groups.

• Also, I expect that the code would die if one of the inputs were an Optional WorkspaceProperty.

Take the behavior of PairedGroupAlgorithm, generalize it to N input workspaces, and use it for default Algorithm behavior.

[mantid-builder]

This issue was originally trac ticket 4647