package/slang: bump version to 2.3.1a

package/slang: bump version to 2.3.1a

Switched to bz2 tarball, upstream does not provide a gz tarball anymore.

Rebased 0001-slsh-libs.patch according to
https://gitweb.gentoo.org/repo/gentoo.git/tree/sys-libs/slang/files/slang-2.3.1-slsh-libs.patch

Removed patches applied upstream:
0002-Enable-a-statically-linked-version-of-slsh.patch
0003-Disable-module-support-in-the-statically-linked-version-of-slsh.patch
0005-make-install-static-do-install-pkgconfig-as-install-.patch

Removed 0004-Rename-posix_close-function-to-posix_close_slfile.patch
after upstream committed a different solution, Alpine Linux did the
same when bumping to 2.3.1:
https://git.alpinelinux.org/cgit/aports/commit/main/slang?id=d4d252e4dea77c868259b0ef1f3d9cfbe6dc2152

Added sha256 hash and license file hash.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
[Arnout: Added sha256 hash and license file hash.]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>