improper handling of neigh edges when loading .net.xml file

[namdre]

if the origional network was computed using option --opposites.guess.fix-lengths (and fixes were applied) then problems occur when reprocessing the net.xml file

• with netconvert, an unequal-length error is generated
• with netedit the error is generated but the network is saved with missing neigh values

[namdre]

The problem is not with the applied fixes (which are mainted using setLoadedLength) but rather with tiny numerical fluctuations (due to output precision) that can make neigh lengths unequel even if they were equal before.