db: Fix typo in the documentation of db::DBMemory class' constructor
db: Fix typos in column declaration (SQL)
db: New version of the database (version 6)

Now there is two possible versions of the code of a bug:
- The initial code is the code is the code that a egg has when it's created.
  This code can be the code of a spawn or a copy of the executable code of
  its father. This initial code of a bug isn't never modified.
- The executable code is the code that the bug is executing while it's alive.
  When the bug died, this code is deleted from the database.

As the initial code can't be modified, the bugs spawned will share the same
code. Also, as the executable code is deleted after the death of a bug, the
database size of this version is lower than the previous version.

As the changes to the database were not compatible, the database version was
increased to 6.
Update the NEWS file with the changes to the database
db: Make db::AliveBug::bug_id() inline
db: Make db::DeadBug::bug_id() inline
Derive sw::Exception from std::exception

If a exception is derived from std::exception, Boost::Test can show a better
error message when a exception is thrown while executing a unit test.
db: Add the SQL needed to create the database for the unit tests
db: Remove unnecesary dependencies for the unit test of the sw::db classes

The libraries simpleworld and simpleworld_cpu are not needed by the unit
tests of the sw::db classes. Removing theese dependencies, those unit tests
can be compiled and executed even if those libraries can't be compiled.
db: Add unit test for db::Code
db: Add unit test for db::Registers
db: Fix wrong exception texts in db::Blob
Don't try to force to get a different word when a word is mutated

When a permutation over a word is done, if this word has the value
of 0x00000000, the new value will have always the same value as the
old one. So, before this change, a infinite loop was done.
With a total or partial mutation the previous loop was ok, but the
loop was deleted too for consistent behaviour with the permutation.
Use the same code_id of the spawn as the code_id of the bug