Patch SFTPFile to be used as an context manager.

paramiko.SFTPClient.open returns a file-like object SFTPFile. SSHConnect
returns an instance of SFTPFile but first patches the class to implement
the context manager protocol (enter and exit methods).
Support for global config (located at ~/.pic/config). All command line
options can also be globally specified, but command line flags take
precedence.

Examples:

[viewer]
prog = gthumb

[backup]
path = /mnt/backup/photos:/home/user/photos