common: Extend function percent_data_escape.
* 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>