to make sure the scripts have not been altered.

the unflushed data when closing file can be several thousand kiloes,
loop until all is written out.

prefer index in the new format as signed .tar.gz.

speeds up digest calculation on some cases.

that got broke during verify implementation.

an utility to check package signature and integrity.

in future we might add datahashalg to specify the algorithm used.

to speed up apk installation avoid calculating checksums.

change the index generation to do old index, or the new style index
where package identity is sha1 of control block and it's contained
within an .tar.gz to allow signing in future.

replace the old 'delete' option, with 'index'. the idea is that
one can provide existing index files to take cached meta-data of
the package from (assumes package has not been modified if index is
newer, and package size has not changed).

this way one always gives the list of .apk files to include in
the new index, and the old index is used only as "cache".

and prefer sha1 checksums to be stored in base64 encoded format.

otherwise we don't get chechksum anymore after the changes to
support partial gzip checksumming.

this also convers scripts file to a tar archive.

was left there unintentionally while debugging stuff.

snprintf is dog slow. make the blob stuff have some helper functions
so we can use them in code paths that are executed often.

avoid recalculating hashes, and store the lengths of names, so
we can optimize some operations.

also make the array code more explicit to have gcc optimizer happy.

some fixes on index reading code too.

in future we want to checksum on gzip boundary basis, not the
full file.

to actually get hardware acceleration if available.

allow .apk to consist of multiple separate gzip streams which
are just concatenated together.

We use APK_UPDATE_CACHE apk_flag instead.

Support for limiting output for only showing the packages who have
the status we are interested in. For example --limit '<' will only
list packages that have a newer version available.

While here, we also fix so packages that are not in any repository
are displayed with '?'.

This will update the repository cache upon db_open.

we need to know if caching is enabled, before the repositories are
added. otherwise the cache is not used properly at db opening time.