lib/survex.pot,src/commands.c: Say "survey" instead of "prefix level"
in the warning about reentering one.
lib/survex.pot,src/commands.c: After 5 warnings about reentering a
survey we give up warning about that, but we used to keep reporting
where the survey was originally entered - this secondary diagnostic
message is now silenced when the main message is.
lib/: Merge changes from survex.pot to the po files.
tests/doubleinc.out: Fix testsuite for change to message in last
commit but one.