Fix the import task on very long key

I was importing translation files with `keys` longer 
than the 255 VARCHAR setted in the entity.

So the search was always returning false because searching with 
a long key something trimed at 255 chars.

That's not the most glorious fix, but the translations 
files I'm working with are not glorious neither. I think 
a 255 chars key is enougth, this PR is only about 
making the imported works with bad translation files.
Merge pull request #12 from damienalexandre/patch-1

Fix the import task on very long key
add option "force" (force update of translations) & argument "bundle" (import translations for this bundle only) to import command
improve the way to get the relative translation file path
update commands
update tests
remove var_dump :D
use mb_substr() instead of substr() =]
Merge pull request #13 from Cethy/symfony2.0

import command enhancements
fix directory separator