Fix wrong jump if no count is specified

If jump next hunk with no count, it move last hunk of below hunks.

v:count step is 0, 2, 3, 4..., so if no count is specified, next hunk is
-1(this is last hunk of below hunks).  Because of above reason, I change
to use v:count1 instead of v:count.  v:count1 step is 1, 2, 3, 4... .

Closes #40.
Make jumping behaviour more pragmatic

This patch makes jumps go the the first/last hunk when the given count
was bigger than the available hunks.

E.g. when there are only 2 hunks and you use 4]c, the cursor jumps to
the last hunk nevertheless. Before this patch the cursor wouldn't move
at all (which mimics the standard behaviour of ]c/[c).

Closes #41.
Merge branch 'fix-jumping'