Sync database are no longer exploded on the filesystem. Rework the logic
used to generate our test databases so we can create them completely in
memory without having to write the individual files to disk at all. The
local database is unaffected.

Note that several shortcomings in libalpm parsing were discovered by
this change, which have since been temporarily patched around in this
test suite:

* archive_fgets() did not properly handle a file that ended in a
  non-newline, and would silently drop the data in this line.
* sync database with only the file entries and not the directories would
  fail to parse properly, and even cause segfaults in some cases.

Signed-off-by: Dan McGee <dan@archlinux.org>