Add test case for new feature of the "rhizome add" command: if the author SID
is not specified (empty arg) then it searches the keyring for the author.
Removed "authorSid" argument from several functions that also take a struct
rhizome_manifest * arg, since the author, if known, is now supplied in the
struct.
Improve return value handling and refactored some rhizome crypto code.
Replace ".selfsigned" column with ".author" and ".fromhere" columns in
output of "rhizome list" command. (Note that a "sender" column is
already present.)
Add 'author' field to struct rhizome_manifest.
Log all fully rendered SQL statements on DEBUG_RHIZOME.
Update 'rhizomeops' test cases and improve the assert_rhizome_list()
test function to be able to assert authorship of files.
Cherry picked from commit e994626429, conflicts
in testdefs.sh resolved manually (start_servald_instances() sets DUMMYx
variable).
Move create_rhizome_identities() from testdefs_rhizome.sh to
create_identities() in testdefs.sh
Rename create_identity() in testdefs.sh to create_single_identity(), uses
create_identities() to do its work.
