Support files created through external editor

[clandrew]

Check that ColumnMode doesn't hard depend on whitespace padding out the document.

[clandrew]

@vdwtanner I tried reproing a problem with this just now, and I couldn't. What I tried

1. Create a document in external editor like Notepad with mixed length lines
2. Open document in ColumnMode
   Result: ColumnMode pads out lines with spaces

Second attempt

1. Update document in external editor remove all trailing whitespace on lines. There's mixed length lines
2. Hit 'Refresh' in ColumnMode
   Result: ColumnMode still pads out the lines with spaces, according to whatever is the longest line

Is there something else to try here?

[clandrew]

Spoke offline- the above was a misunderstanding about what was going on. Updated bug title to reflect what is actually being asked for