Properly handle spacing around operators in second column of aligned and gathered environments. Issue #982
Take base.x into account for positioning of super ans subscripts.  Resolves issue #966.
Handle linebreaking in a base with empty superscript or subscript.  Resolves issue #949.
Merge branch 'issue982' into develop.  Issue #982.
Merge branch 'issue966' into develop.  Issue #966.
Merge branch 'issue949' into develop.  Issue #949.