option to disable auto flush

[dbu]

in Adapter/Gaufrette/CmfMediaDoctrine.php we have to flush after each write as gaufrette clients expect a file system behaviour. on the other hand, most of the time there will only be one operation i guess? if we go though a web interface, we upload 1 file or delete 1 file or edit 1 file, not several at once. so i guess its not that important all in all.

as the write methods will be called by generic code not knowing or caring about the optional flush parameter, we should have another way to handle this. i would propose we have a global config option on this class whether to autoflush (expected gaufrette behaviour) or not and expose some sort of getObjectManager method so that the user can flush it if needed. such as a method setAutoFlush(false)

see also #5 and KnpLabs/Gaufrette#186

[dbu]

fixed in #27