adjust filtering of mysql binary tarballs

- Now filter static libraries and embedded/debug binaries from ./bin
  Previously ./mysql-test ./sql-bench files were filtered
- Resolves issue #6
minor tweak to README verbiage
allow a directory to specified for --data-source

- If a directory is specified, dbsake will replace $sbdir/data with
  a symlink to the specified directory
- If a directory is specified, some "best effort" is done to check
  that datadir is not already in use by attempting a shared read
  lock on the ib_logfile0 file
Merge branch 'develop' into feature/sandbox_from_datadir
Merge branch 'feature/sandbox_from_datadir' into develop
fix discrepancy between --data and --data-source in docs

- documentation had some stale references to --data which was
  an early incarnation of --data-source in 1.0.4 builds. This
  has been fixed and only --data-source should be referenced.
update documentation for --data-source to reflect changes

- Added documentation noting that --data-source now accepts
  a datadir. Resolves issue #4.
- Clarified documentation about --data-source from tarballs
  somewhat.