Next to including several files, our "common.h" header also declares
various macros which are then used throughout the project. As such, we
have to make sure to always include this file first in all
implementation files. Otherwise, we might encounter problems or even
silent behavioural differences due to macros or defines not being
defined as they should be. So in fact, our header and implementation
files should make sure to always include "common.h" first.

This commit does so by establishing a common include pattern. Header
files inside of "src" will now always include "common.h" as its first
other file, separated by a newline from all the other includes to make
it stand out as special. There are two cases for the implementation
files. If they do have a matching header file, they will always include
this one first, leading to "common.h" being transitively included as
first file. If they do not have a matching header file, they instead
include "common.h" as first file themselves.

This fixes the outlined problems and will become our standard practice
for header and source files inside of the "src/" from now on.

OpenSSL v1.1 has introduced a new way of initializing the library
without having to call various functions of different subsystems. In
libgit2, we have been adapting to that change with 88520151f
(openssl_stream: use new initialization function on OpenSSL version
>=1.1, 2017-04-07), where we added an #ifdef depending on the OpenSSL
version. This change broke building with libressl, though, which has not
changed its API in the same way.

Fix the issue by expanding the #ifdef condition to use the old way of
initializing with libressl.

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>

Previous to OpenSSL version 1.1, the user had to initialize at least the error
strings as well as the SSL algorithms by himself. OpenSSL version 1.1 instead
provides a new function `OPENSSL_init_ssl`, which handles initialization of all
subsystems. As the new API call will by default load error strings and
initialize the SSL algorithms, we can safely replace these calls when compiling
against version 1.1 or later.

This fixes a compiler error when compiling against OpenSSL version 1.1 which has
been built without stubs for deprecated syntax.

Up to version 1.0, OpenSSL required us to provide a callback which implements
a locking mechanism. Due to problems in the API design though this mechanism was
inherently broken, especially regarding that the locking callback cannot report
errors in an obvious way. Due to this shortcoming, the locking initialization
has been completely removed in OpenSSL version 1.1. As the library has also been
refactored to not make any use of these callback functions, we can safely remove
all initialization of the locking subsystem if compiling against OpenSSL version
1.1 or higher.

This fixes a compilation error when compiling against OpenSSL version 1.1 which
has been built without stubs for deprecated syntax.

The OpenSSL library may require multiple locks to work correctly, where
it is the caller's responsibility to initialize and release the locks.
While we correctly initialized up to `n` locks, as determined by
`CRYPTO_num_locks`, we were repeatedly freeing the same mutex in our
shutdown procedure.

Fix the issue by freeing locks at the correct index.

Error messages should be sentence fragments, and therefore:

1. Should not begin with a capital letter,
2. Should not conclude with punctuation, and
3. Should not end a sentence and begin a new one

add support for OpenSSL 1.1.0 for BIO filter

For older versions we can fall back on the deprecated ASN1_STRING_data.

We want to program against the interface, so recreate it when we compile
against pre-1.1 versions.