Log Message:
Update netpgpverify and libnetpgpverify to 20160705

External API changes
====================
+ add a pgpv_cursor_close() function to free resources associated with
a cursor

Better memory management
========================
+ restructure the way dynamic arrays are used, to avoid memory
corruption issues and memory leaks - keep all dynamic arrays in the global
data structure, and use indices in the other data structures to index them.
Means lack of data localisation, but avoids stale pointers, and leaks.

+ make signer field of signature a uint8_t array, rather than a pointer

+ use our own version of strdup(3) - don't depend on it being
available in standard library

+ keep track of whether litdata filenames and userid were allocated or not,
and free memory in pgpv_close() if it was allocated

+ free up allocated resources which were allocated in pgpv_close()