[xmlsec] Library versioning

[Scott Cantor]

Noticing the recent comments about .so versions, do yourself a favor and make sure you adhere to this spec:

http://sources.redhat.com/autobook/autobook/autobook_91.html#SEC91

A lot of projects (e.g. OpenSSL) do not, and it's a serious pain in the butt to deal with in many cases. I expect the excuse tends
to be "we're not at 1.0 yet, so it doesn't matter", but if it's in wide usage before 1.0, then that's enough to justify doing the
right thing.

-- Scott