Add function npth_is_protected.
* src/npth.c (got_sceptre): New. (enter_npth, leave_npth): Set. (npth_is_protected): New. * w32/npth.c: (got_sceptre): New. (enter_npth, leave_npth): Set. (npth_is_protected): New. * w32/npth.def, src/libnpth.vers: Add new function.
- Signed-off-by: Werner Koch <wk@gnupg.org>