prevent with-embedded-cryptopp builds from using object files from without-embedded-cryptopp builds or vice versa

[zooko]

<zooko> if you run python setup.py build it builds a bunch of C++ files with
	certain #include's and then links them with -lsomelib.
<zooko> If you run python setup.py build --disable-embedded-cryptopp then it
	builds them with different #includes and links them to a different
	-lsomelib.
<zooko> Unfortunately, if there are still .o files from an earlier build that
	had a different setting for that flag then those .o's were build with
	the wrong #includes.					        [23:16]
<zooko> If I were using make, I would tell make that the .o files depended on
	the --disable-embedded-cryptopp flag somehow.
<zooko> Actually I'm not sure how I would do that in make, either.
<merwok> Hm, reminds me of an infixable bug in distutils	        [23:17]
<zooko> If I could tell it that the name of the temporary "build" dir where it
	should look for .o files has to be different depending on the setting
	of the --disable-embedded-cryptopp flag, that would solve it.
<merwok> zooko, you can, in a build_ext subclass
<zooko> merwok: aha, that sounds promising.
<merwok> zooko: Otherwise you may hit http://bugs.python.org/issue10374
								        [23:18]
<zooko> merwork: if I have a build_ext subclass, 
<zooko> how do I change the name of the dir in which it looks for .o's?
								        [23:19]
<merwok> Looks like a default value for build_dir (or build_base, or
	 build_temp) in finalize_options
<merwok> Of course, they can be built in place too, you may want to reject
	 that option.