* pinentry/pinentry.c: Include <assert.h>.
(pinentry): Set pin_len to 0.
(pinentry_setbufferlen): If len is less than 2048, set it to 2048.
Add an assertion.
(pinentry_setbuffer_clear): New function that releases the pin buffer.
(pinentry_setbuffer_init): New function that initializes the pin
buffer.
(cmd_getpin): Use pinentry_setbuffer_init and pinentry_setbuffer_clear
instead of manual memory management.
(cmd_confirm): Use pinentry_setbuffer_clear instead of manual memory
management.