lines with different clearances should not be merged

[tsaitgaist]

Problem:
When multiple lines (with same direction, thickness, and clear flags) and moved, they are merged as one line.
Only the clearance of the first line is used for the merged line.
This behaviour is not wished when the lines have different clearances.
Solution:
Verify the lines clearances and only merge lines if they hace the same clearance.

[tsaitgaist (kevredon)]

this applies to pcb 20110918 and current git c8b51a09905fb3bf8dba2eaaef99e2bc76b2d18a (Sun 02 Dec 2012 03:13:30 PM CET)

[Peter Clifton (pcjc2)]

Applied (slightly modified) as commit c83cec94d723080881340012f1b9e1a314e17da7

Thanks!