re-arrange the build support structures to ease migration to the revised

ZConfig-using zpkg; this will help keep the build-support stuff out of the
top-level directory of the checkout (such is the plan, at least)

buildsupport/README.txt

+zpkg support files
+==================
+
+Files and packages included here are intended to support the use of
+zpkg as a build tool.  They are not part of Zope, are not included in
+the distribution, and are not importable in the application server.
+
+The setup.py script will process any .pth files placed here, though
+those would not normally be handled by most applications.

setup.py

@@ -13,6 +13,15 @@
 ##############################################################################
 
 import os
+import site
+import sys
+
+here = os.path.dirname(os.path.abspath(__file__))
+buildsupport = os.path.join(here, "buildsupport")
+
+sys.path.insert(0, buildsupport)
+# Process *.pth files from buildsupport/:
+site.addsitedir(buildsupport)
 
 import zpkgsetup.package
 import zpkgsetup.publication
@@ -21,9 +30,6 @@ import zpkgsetup.setup
 # Note that release.py must be able to recognize the VERSION line.
 VERSION = "3.5.0a8"
 
-
-here = os.path.dirname(os.path.abspath(__file__))
-
 context = zpkgsetup.setup.SetupContext(
     "ZODB", VERSION, __file__)