build: add the prebuild command as a dependency for develop

So, 'python setup.py develop' exists. And of course it doesn't have build_py as
a dependency, because of course it doesn't.
We could use 'data_files' instead of 'package_data and copying', and then use
pkg_resources to find the actual file location, and that could work in theory.
But pkg_resources API is weird and messy and this whole area of Python
packaging theory barely works as it is.

Instead we will force the prebuild command to be a dependency of develop as
well as build_py, and we do this by monkey-patching instead of the proper way,
because at this point it seems cleaner. I wonder if there are more commands
that would need this.

setup.py

@@ -5,6 +5,7 @@ import subprocess
 
 from setuptools import setup, Command
 from setuptools.command.build_py import build_py
+from setuptools.command.develop import develop
 
 install_requires = [
     'setuptools>=19.0',
@@ -61,10 +62,19 @@ class PrebuildCommand(Command):
             print("Using pre-generated files.")
 
 
-class CustomBuild(build_py):
-    def run(self):
+def _patch_prebuild(cls):
+    """Patch a setuptools command to depend on `prebuild`"""
+    orig_run = cls.run
+
+    def new_run(self):
         self.run_command('prebuild')
-        super().run()
+        orig_run(self)
+
+    cls.run = new_run
+
+
+_patch_prebuild(build_py)
+_patch_prebuild(develop)
 
 
 setup(
@@ -99,6 +109,5 @@ setup(
     ],
     cmdclass={
         'prebuild': PrebuildCommand,
-        'build_py': CustomBuild,
     },
 )