Xerces-C++ header installation

My stubborn re-posting and repeated re-explaining in the Xerces-C++ mailing list has finally paid off with a response
from a maintainer and a vote that’s underway. The issue?
Putting the include files under prefix/include/xercesc
instead of prefix/include. Such a minor thing has taken a
ridiculous amount of effort. I believe that it’s partly due
to the fact that there’s not 1 or 2 maintainers, but a set
of many people of varying responsibility. If there was any
alternative C++ XML parser then I would have walked away
from this in frustration. It’s very unfortunate because the
actual source code of Xerces-C++ is wonderful.

I don’t look forward to the same thing over the issues of
proper versioning, binary/API compatibility between stable
releases, release planning, and binary packaging for
distributions. The lesson? Just do things the standard way
from the start. Use autoconf/automake.