Previously, the install stage would compile in things that were
disabled during the build_ext phase. This would also result in the
build pulling in locally installed versions of libraries that were
disabled. The install process doesn't honor the same command-line
flags that build_ext does, but does call build_ext again. Avoid the
whole issue by just writing the options to setup.cfg
Also, add the Imagemagick dependency for tests.
b072caadec