avoid setting innodb-log-files-in-group to empty string

- This looks like a dumb 2.0 regression - now only set this
  option in the my.sandbox.cnf if > 2 and set to 2 by default
  so we maintain sane defaults.
set MY_BASEDIR_VERSION in sandbox.sh

- This makes sandbox.sh more compatible with 5.0/5.1 mysqld_safe
  and allows sandbox.sh to be more more reliably run outside of
  the sandbox directory, where older mysqld_safe scripts might
  otherwise fail to find the MySQL utilities.
  Resolves issue #66
add trailing newlines to my.sandbox.cnf and sandbox.sh

- minor, but annoying, regression due to jinja2 behavior. This
  ensures a trailing newline is written at the end of these
  generated files.  jinja2 2.7+'s keep_trailing_newline option
  is not used for compatibility with older versions to make
  RPM / deb deployments easier.