Update to JSch 0.1.51

Closes #78.
(cherry picked from commit 537b69d)
(cherry picked from commit 85d3344)
(cherry picked from commit a147a13)
Clean tests and use hamcrest

Closes #79.
(cherry picked from commit b5aaa51)
(cherry picked from commit 237c63e)
(cherry picked from commit b99d39c)