* use `calloc()` to allocate zero-initialized structs.
* order the allocation of members by their declaration.
* order the freeing of members in reverse order.
* move init of `silent` flag in plugin case.
* fix double free of `tmpname` in `aesgcm_file_get()`.
* make some functions static.
Signed-off-by: Steffen Jaeckel <s@jaeckel.eu>