Update soname

[Anthony Green]

(I've CC'd Benjamin and Uli who really understand this stuff)

Bryce wrote:
> No, good idea. We should probibly make it "libgcj.so.3.0.0" to make it
> clear what release the libgcj came from.

This is the versioning scheme that the libtool authors warn against in their
manual.  The suggest that it's better not to even try to keep these version
numbers in sync.

It will become confusing if, for instance, we're forced to go to
libgcj.so.4.a.b for GCC 3.c.

I don't know what the right solution is.  One idea is to actually try to
maintain the version numbers according to the libtool manual, even during
development.

libstdc++ also has a configure option to include the GCC version number into
soname.  They seem to have put lots of thought into this.  Perhaps, if it
makes sense, we should just adopt the policies that they use.

AG