Add a boundary to parse_patches()

This is useful since specifying the ".." range would generate all the
applied and unapplied patches for commands like "show" and
"delete". With this patch, the boundary is crossed only if
specifically asked (i.e. the first and last patch of the range are on
each side of the boundary).

Signed-off-by: Catalin Marinas <catalin.marinas@gmail.com>