The clone options contain fields for ae remote create callback
and its payload, which can be used to override the behavior when
the default remote is being created for newly cloned
repositories.
Currently we only accept a C function as callback, though, making
it overly complicated to use it. We also unconditionally `free`
the payload if its address is non-`nil`, which may cause the
program to segfault when the memory is not dynamically allocated.
Instead, we want callers to provide a Go function that is
subsequently being called by us. To do this, we introduce an
indirection such that we are able to extract the provided
function and payload when being called by `git_clone` and handle
the return values of the user-provided function.
Some test repositories are not correctly removed after the tests
did run. Fix by introducing a function that is to be used for
cleaning up temporary test repositories.
Patrick Steinhardt
Carlos Martín Nieto
Jesse Ezell