Update build environment to fix VPATH support.

  make depend, make tests, and make install all work when build directory
  is not the $srcdir.
Also modified library handling such that -lpthread more likely to be last.
WARNING: new orderring requires use of LDFLAGS to set global loader options
  such as -L/usr/local/lib.  If you put this in LIBS, some libraries
  may not be found a link time.
Likely broke Kerberos/LDAPD support.  Don't have those in my testbed.