This change makes all non-user-creatable structures non-comparable. This
makes it easier to add changes later that don't introduce breaking
changes from the go compatibility guarantees perspective.
This, of course, implies that this change _is_ a breaking change, but since
these structures are not intended to be created by users (or de-referenced),
it should be okay.
Using `StatusOptions.Pathspec` results in a fatal error panic with
the message 'unexpected signal during runtime execution'.
This is because the `&cpathspec` C.git_strarray gets freed in
`*StatusOptions.toC()` before being passed to
`C.git_status_init_options()` in `*Repository.StatusList()`
(see b3e7705c48/status.go (L138))
The relevant panic trace is:
```
fatal error: unexpected signal during runtime execution
[signal 0xb code=0x1 addr=0xb01dfacedebac1e pc=0x4062609]
runtime stack:
runtime.throw(0x469a080, 0x2a)
/usr/local/Cellar/go/1.5.1/libexec/src/runtime/panic.go:527 +0x90
runtime.sigpanic()
/usr/local/Cellar/go/1.5.1/libexec/src/runtime/sigpanic_unix.go:12
+0x5a
goroutine 71 [syscall, locked to thread]:
runtime.cgocall(0x400a720, 0xc8204e9998, 0x0)
/usr/local/Cellar/go/1.5.1/libexec/src/runtime/cgocall.go:120 +0x11b
fp=0xc8204e9968 sp=0xc8204e9938
github.com/libgit2/git2go._Cfunc_git_status_list_new(0xc8204c39c8,
0x5e17780, 0xc820478c40, 0xc800000000)
??:0 +0x39 fp=0xc8204e9998 sp=0xc8204e9968
github.com/libgit2/git2go.(*Repository).StatusList(0xc820013290,
0xc8204e9b58, 0x0, 0x0, 0x0)
/Users/calin/go/src/github.com/libgit2/git2go/status.go:168 +0x11d
fp=0xc8204e99e8 sp=0xc8204e9998
```
While Go will assign the correct type to a const block when it
auto-creates the values, assigning makes the const be typeless and will
only gain it in each particular use.
Make each constant in the blocks have an assigned type.