gschem: Changed behavior of enter key in entry widgets

In the line properties dialog box, the enter key applies the value and
moves the focus downward in the column of widgets.
gschem: Only update selection when entries change

Entrys must ubdate the selection when the focus leaves the widget.
This change will only update the selection when the user changes
the data in the widget.
gnetlist: Safer use of nettattrib-generated refdes.

Two-pronged attack to make gnetlist's use of autogenerated "POWER"
refdes less likely to cause a problem.

1) Use a longer, more specific prefix string.  This will make it much
   much less likely that a collision with a user net name will occur.

2) When testing for autogenerated refdes, test for the exact prefix
   using strncmp() instead of just checking that it appears somewhere
   in the string.

Affects-bug: lp-1226246

(imported from commit c58247b598517b875d8cb2b80eb812e92ee9c87f)
gnetlist: Error on clashes with netattrib-generated refdes.

Exit with an error if a refdes is found in input files that conflicts
with autogenerated netattrib-related refdes.

Closes-bug: lp-1226246

(imported from commit dcd9b1c6eb472b80117d945896c56092acfdeac7)