Work around pip issue #1630 breaking 'pip -e git+url'

https://github.com/pypa/pip/issues/1630

Fixes ticket #18 (opened in 2010!)

NEWS

@@ -4,6 +4,8 @@ Current release
 What's new in psycopg 2.5.3
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
+- Work around `pip issue #1630 <https://github.com/pypa/pip/issues/1630>`__
+  making installation via ``pip -e git+url`` impossible (:ticket:`#18`).
 - Added arbitrary but stable order to `Range` objects, thanks to
   Chris Withers (:ticket:`#193`).
 - Avoid blocking async connections on connect (:ticket:`#194`). Thanks to

setup.py

@@ -507,9 +507,11 @@ you probably need to install its companion -dev or -devel package."""
 
 # generate a nice version string to avoid confusion when users report bugs
 version_flags.append('pq3') # no more a choice
+
 for have in parser.get('build_ext', 'define').split(','):
     if have == 'PSYCOPG_EXTENSIONS':
         version_flags.append('ext')
+
 if version_flags:
     PSYCOPG_VERSION_EX = PSYCOPG_VERSION + " (%s)" % ' '.join(version_flags)
 else:
@@ -530,6 +532,13 @@ if parser.has_option('build_ext', 'static_libpq'):
 else:
     static_libpq = 0
 
+# And now... explicitly add the defines from the .cfg files.
+# Looks like setuptools or some other cog doesn't add them to the command line
+# when called e.g. with "pip -e git+url'. This results in declarations
+# duplicate on the commandline, which I hope is not a problem.
+for define in parser.get('build_ext', 'define').split(','):
+    define_macros.append((define, '1'))
+
 # build the extension
 
 sources = [ os.path.join('psycopg', x) for x in sources]