Make it easier to use stream wrappers for file/image/media attributes, or at least load them transparently from remote servers

[gggeek]

See f.e. the sftp wrappers: http://php.net/manual/en/wrappers.ssh2.php.

1. current code which deals with looking files up in 2 paths does not really play well with using something akin to ssh2.sftp://user:pwd@server:port/remote/file.txt as base path

2. some stream wrappers need to inject the context in order for the fopen call to succeed (see: http://be2.php.net/manual/en/function.ssh2-sftp.php)

3. even if the stream wrapper is properly set up on the side of the of the ComplexField, it probably won't work anyway unless the file is copied locally due to code in the eZ5 Field types. In which case we do have to take it upon ourselves to do that...

[gggeek]

Note: in version 4 with the new 'file' Executor the above scenario might have already become possible or at least somewhat easier