Stash was sometimes obscuring the actual error code, replacing it
with a -1 when there was more descriptive value. This updates
stash to preserve the original error code more reliably along
with a variety of other error handling tweaks.
I believe this is an improvement, but arguably, preserving the
underlying error code may result in values that are harder to
interpret by the caller who does not understand the internals.
Discussion is welcome!
Without this change, any failed assertion in the second (or a later) test
inside a test suite has a chance of double deleting memory, resulting in
a heap corruption. See #1096 for details.
This leaves alone the test cases where we "just" use cl_git_sandbox_init()
and cl_git_sandbox_cleanup(). These methods already take good care to not
double delete a repository.
Fixes#1096
