* src/http.c (metalink_from_http): Fix hash_bin_len type. Use ssize_t
instead than size_t. Reject -1 as base64_decode() return value
* testenv/Makefile.am: Add new file
* testenv/Test-metalink-http-baddigest.py: New file. Metalink/HTTP
malformed base64 Digest header tests
On malformed base64 input, ssize_t base64_decode() returns -1. Such
value is too big for a size_t variable, and used as xmalloc() value
will exaust all the memory.
