gpt: return size of created strings in to_utf8/to_ucs2.

gpt: Fixed a number of remaining issues.

* The header and table is now correctly written; the backup is still
missing, though.
* The Header class is now responsible for both, the primary, and the
backup header.
* Changed the Header constructors: the block is no longer needed. Also,
under GCC 4 the initialization code accidentally used the read
Header constructor.
* Fixed incorrectly copied GUID - the static_guid cannot be copied
into a guid_t directly.
* Fixed copy&paste bug that would overwrite the offset for the child
partition to be created.
* With all of this in place I successfully created a BFS partition
with a GUID partition table. However, I have not yet tested if other
systems can still read this. Also, creating two partitions doesn't
seem to work yet, either (luckily I only need a single one ;-)).

Implemented write support, reorganized source files.

* Moved some functionality into their own files so that they can easily
be reused by other code.
* Added crc32() function from FreeBSD. Implemented CRC handling and
validation.
* Implemented missing write functionality.

gpt: Fixed a number of remaining issues.

* The header and table is now correctly written; the backup is still
missing, though.
* The Header class is now responsible for both, the primary, and the
backup header.
* Changed the Header constructors: the block is no longer needed. Also,
under GCC 4 the initialization code accidentally used the read
Header constructor.
* Fixed incorrectly copied GUID - the static_guid cannot be copied
into a guid_t directly.
* Fixed copy&paste bug that would overwrite the offset for the child
partition to be created.
* With all of this in place I successfully created a BFS partition
with a GUID partition table. However, I have not yet tested if other
systems can still read this. Also, creating two partitions doesn't
seem to work yet, either (luckily I only need a single one ;-)).

Implemented write support, reorganized source files.

* Moved some functionality into their own files so that they can easily
be reused by other code.
* Added crc32() function from FreeBSD. Implemented CRC handling and
validation.
* Implemented missing write functionality.