setup.py: improve debuggability

protocol/setup.py

@@ -6,10 +6,14 @@ import subprocess
 import sys
 
 protoc = find_executable('protoc')
+if protoc is None:
+    print('protoc not found', file=sys.stderr)
+    sys.exit(1)
 
 makedirs('protocol', exist_ok=True)
 protoc_command = [protoc, '--python_out=protocol', 'hello.proto']
 if subprocess.call(protoc_command) != 0:
+    print('could not generate sources by calling protoc', file=sys.stderr)
     sys.exit(1)
 
 setup(name='protocol',