The library stores error information in thread-local storage, which
means we need to make sure that the Go runtime doesn't switch OS
threads between the time we call a function and th time we attempt to
retrieve the error information.
Don't name the return values, as they conflict with the names we want
inside and the types don't match what we want to have inside. We need
them to be two-way channels in the function, and then pass
unidirectional references to the different functions.
Unfortunately libgit2 sometimes returns an error without setting an
error message. Provide an alternative message instead of trying to
dereference nil.
Jesper Hansen
Carlos Martín Nieto
Aidan Nulman
Vicent Martí
Axel Wagner
Vicent Marti