get binbuild working when apr, apr-util, and expat are built shared in

get binbuild working when apr, apr-util, and expat are built shared in
directories that are not well known to the loader.

How it works:
* libtool figures out the name of this system's library path environment
  variable (i.e. LD_LIBRARY_PATH, LIBPATH, DYLD_LIBRARY_PATH) at apr
  configure time (existing code)
* save this variable name in SHLIBPATH_VAR in APRVARS
* substitute this name when apachectl is created
* uncomment the lines containing this variable during binbuild
* install_bindist.sh updates the path to lib/ when the binary is
  installed (existing code)

not done yet, but a good idea:
* create a file or directory containing all environment variable settings
  for apachectl.  Others env vars need to be tweaked, at least on AIX and
  OS/390, so keeping them separate should reduce headaches long term.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@92299 13f79535-47bb-0310-9956-ffa450edef68