* common/percent.c (percent_data_escape): Add new args prefix and
plus_escape.
* agent/command.c (cmd_put_secret): Adjust for changed function
* common/t-percent.c (test_percent_data_escape): Extend test for the
prefix.
(test_percent_data_escape_plus): new test for the plus escaping.
Signed-off-by: Werner Koch <wk@gnupg.org>