[sldev] Patch - Cursor keeps desired X position in Text Editors

[Zi Ree]

Hi Second Life Developers!

Another early patch of mine adapted to the current code base and put up on 
Jira:

Navigating the cursor up and down through a text editor makes the cursor jump 
to the end of line when the line is shorter than the previous one. Moving 
back to the previous line should restore the previous cursor position as 
well. The cursor should always try to keep its X position, regardless of any 
shorter lines traveled through in the meantime.

Jira Entry: https://jira.secondlife.com/browse/VWR-682

Yours,
Zi!