vegbien_dest callers: Removed no longer needed explicit setting $prefix to "", because this is now the default value

vegbien_dest: Changed default $prefix to "", so that the majority of callers don't need to manually set $prefix to "" to avoid it defaulting to out_

README.TXT: Data import: Use env var $version, which is now set by import_all, instead of manually inserting the version for <version>

vegbien_dest: Also export $version

import_all: Run the import directly into a new, already-versioned public schema. This removes the need to manually rename the schema after import, and allows the backup commands to use the stored $version shell variable to refer to the last import.

schemas/Makefile: %/publish: Added instruction to run `unset version` after the command, to clear the $version shell variable which will be set by import_all

README.TXT: Data import: Replaced <import_name> with <version> because the import name is now just the version

README.TXT: Data import: Replaced r<revision> with <version> because the version string is now equal to r<revision>

README.TXT: Backups: Replaced <date> with <version> because the date is no longer included in the version string

README.TXT: Name archived imports without the "public." prefix so that their backups will work with the new `make backups/%.backup/remove` command, which does not add back the prefix