Add the _RELEASE global variable to get the Lua release version number

Hi,

Some of the lua error messages are different between the 5.4.2 and the

5.4.3 releases. This breaks the Vim lua tests (as it checks for specific

lua error messages) as reported in the following bug report:

Describe the bug Some lua tests: Failures: From test_lua.vim: Found errors in Test_lua_blob(): command line..scr...

The Vim lua test script uses the _VERSION variable to get the Lua version

and checks for specific error messages based on the Lua version.

But this variable contains only the major and minor Lua version numbers.

So this check fails to differentiate between the 5.4.2 and the 5.4.3 versions.

Running the "lua -v" command displays the major, minor and release version

numbers. But using this command from the Vim test script may give the

incorrect Lua version number, because the lua version in the PATH may

be different from the Lua version Vim is linked against or in some cases

the Lua executable may not be present in the PATH.

To address this correctly, we will need to add a new global variable

called _RELEASE that contains the major, minor and the release

version numbers.

I am attaching a patch to add this global variable.

Regards,

Yegappan