Replace str_to_uint() with str_to_uint32()

Also str_to_int() with str_to_int32()
Replace config 'rhizome.external_blobs' with 'rhizome.max_blob_size'
Add Rhizome db blob primitive functions

sqlite_blob_open_retry()
sqlite_blob_write_retry()
sqlite_blob_close()
Support streaming directly into Rhizome store

The rhizome_open_write() function now accepts RHIZOME_SIZE_UNSET as the
payload size, and streams into an external blob until finished, then
copies the external blob into the FILEBLOBS table if it is small enough.

Needed so that HTTP GET /restful/rhizome/insert can stream the payload
directly into the DB even if the supplied manifest does not specify
'filesize'.
UNFINISHED Implement HTTP POST /restful/rhizome/insert