Implementation of new dump tag and length standard

Implementation of new dump tag and length standard

The implementation follows the specification from October 2007.

All old tags are accecpted as before.
New tags 0x06-0x60 (capital letters) are followed by a 1 byte length
field which may contain directly the length (up to 127) or the length
of the then following length field (max 8) ored with 0x80.
New tags 0x61-0x77a are directly followed by 4 bytes building a 32bit
integer.
0x7b-0xf are single-byte tags, 0x7e meaning next tag is critical.

On this basis unknown tags can be skipped unless they were marked
critical. In this case the restore is aborted.

in dump.h tags following the new standard are marked by an asterisk

Last update: added parameter types for HandleUnknownTag.

Reviewed-on: http://gerrit.openafs.org/191
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>