fix(editor): a slip goes to the crossing under the cursor or nowhere, shown before the click

A slip went to the crossing of the selected straight with another straight within 40 m of the click. When the track under the cursor wasn't taken as a straight (a slight curve, a switch), the slip silently went to another crossing up to 40 m away. A double slip within 25 m of the click was replaced, even when the click was on a free crossing.

- The crossing nearest the cursor, within 12 m, is found among all the rail tracks. A slip goes only there; when that track is a curve or a switch, the tool says so.
- A double slip is replaced only when it is nearer the cursor than any crossing.
- The cursor is taken at the height of the straight under it, so on a grade the 3D view doesn't put the click metres away from the track.
- Before the click, the view marks the crossing the slip goes to, with its two straights, or the reason it can't go there.

lang/editor_pl.po

@@ -9919,3 +9919,18 @@ msgstr "Tor leży wyżej lub niżej, niż według NMT jest grunt, o więcej niż
 
 msgid "Against the terrain model"
 msgstr "Także względem NMT"
+
+msgid "No track crosses the selected straight under the cursor"
+msgstr "Pod kursorem żaden tor nie przecina zaznaczonej prostej"
+
+msgid "The track crossing here is a switch: a slip goes only where two straights cross"
+msgstr "Tor, który tu przecina, jest rozjazdem: rozjazd krzyżowy stawia się tylko na przecięciu dwóch prostych"
+
+msgid "The track crossing here isn't straight: a slip goes only where two straights cross"
+msgstr "Tor, który tu przecina, nie jest prosty: rozjazd krzyżowy stawia się tylko na przecięciu dwóch prostych"
+
+msgid "Click: this double slip is replaced by the one chosen"
+msgstr "Klik: ten rozjazd krzyżowy zostanie zastąpiony wybranym"
+
+msgid "Click: it goes here"
+msgstr "Klik: stanie tutaj"