We were missing this test on Windows, which meant we didn't notice that
we never fixed the single authentication attempt it tries, nor its wrong
return code.

Enable this for the unix platforms as well over HTTP. We previously were
doing it locally but disabled it on OS X due to issues with its sshd not
accepting password authentication.

We commonly have to check if a git_buf has been allocated
correctly or if we ran out of memory. Introduce a new macro
similar to `GITERR_CHECK_ALLOC` which checks if we ran OOM and if
so returns an error. Provide a `#nodef` for Coverity to mark the
error case as an abort path.

Coverity does not comprehend the connection between a vector's
size and the contents pointer, that is that the vector's pointer
is non-NULL when its size is positive. As the vector code should
be reasonably well tested and users are expected to not manually
modify a vector's contents it seems save to assume that the
macros will never dereference a NULL pointer.

Fix Coverity warnings by overriding the foreach macros with
macros that explicitly aborting when (v)->contents is NULL.

When checking if a string is prefixed by a drive letter (e.g.
"C:") we verify this by inspecting the first and second character
of the string. Coverity thinks this is a defect as we do not
check the string's length first, but in fact we only check the
second character if the first character is part of the alphabet,
that is it cannot be '\0'.

Fix this by overriding the macro and explicitly checking the
string's length.

Add nodefs for macros that abort the current flow due to errors.
This includes macros that trigger on integer overflows and for
the version check macro. This aids Coverity as we point out that
these paths will cause a fatal error.

When posting our instrumented build results to Coverity we have
to include sensitive information, in particular our authorization
token. Currently we use an unencrypted channel to post this
information, leading to the token being transferred in plain.

Fix this by using a secured connection instead.

Coverity currently lists a lot of errors with regard to
GITERR_CHECK_ALLOC causing resource leaks. We know this macro is
only invoked when we want to abort because we are out of memory.

Coverity allows for overriding the default model where we know
that certain functions guarantee a desired behavior. The
user_nodefs.h is used to override the behavior of macros.
Re-define GITERR_CHECK_ALLOC inside of it to specify its abort
nature.

Homebrew will error out because it's already installed.

We need to make sure we are asking for the current version of packages,
or we might get 404s from the download service.