Builtins plugin work:
- Recursive invocations (unix -r et al) were not handled properly:
every new invocation allocated the new mem pool, making the previous
pool unaccessable. Now only one pool is allocated. Refcounting added
to know when the pool is safe to destroy.
- The above is an incompatible change for generic.S. Introduced the
builtins interface versioning. Now if dosemu detects the outdated
version of builtins, it will not run them and will ask user to upgrade.
- Removed the code that was intended to allow calling builtins with
far call. This code was never used and was broken since generic.S
started to release memory at startup.
- Moved DOS version checking from builtins.c to lredir.c.


git-svn-id: https://dosemu.svn.sourceforge.net/svnroot/dosemu/trunk@648 7758b857-130e-0410-ab9c-d8735a528d18