sftp: Reset eof on seek operations.
sftp: Reset eof on seek operations.

This fixes bug #48.
(cherry picked from commit c483418b8210bc47a765f6b0e0dc99aec63e80fd)

mwgoldsmith/libssh,mwgoldsmith/libssh,mwgoldsmith/libssh,mwgoldsmith/ssh,mwgoldsmith/ssh,mwgoldsmith/ssh,mwgoldsmith/libssh,mwgoldsmith/ssh