Cygwin support

[wlnirvana]

The current release seems not supporting Cygwin platform. I got the error below.

$ uname -a
CYGWIN_NT-6.1 Dell 1.7.33-2(0.280/5/3) 2014-11-13 15:47 x86_64 Cygwin
$ python setup.py build
Don't know how to compile leveldb for CYGWIN_NT-6.1!

The latest leveldb has added support fow Cygwin, see here, though I recently found it's not working sometimes.

I managed to install py-leveldb on Cygwin after I applied the following changes:

$ git diff
diff --git a/leveldb/port/port_posix.h b/leveldb/port/port_posix.h
index f2b89bf..4667921 100644
--- a/leveldb/port/port_posix.h
+++ b/leveldb/port/port_posix.h
@@ -55,7 +55,7 @@

 #if defined(OS_MACOSX) || defined(OS_SOLARIS) || defined(OS_FREEBSD) ||\
     defined(OS_NETBSD) || defined(OS_OPENBSD) || defined(OS_DRAGONFLYBSD) ||\
-    defined(OS_ANDROID) || defined(OS_HPUX)
+    defined(OS_ANDROID) || defined(OS_HPUX) || defined(CYGWIN)
 // Use fread/fwrite/fflush on platforms without _unlocked variants
 #define fread_unlocked fread
 #define fwrite_unlocked fwrite
diff --git a/setup.py b/setup.py
index 9413d89..860eb94 100644
--- a/setup.py
+++ b/setup.py
@@ -38,6 +38,14 @@ elif system == 'Linux':
         '-DOS_LINUX',
         '-DLEVELDB_PLATFORM_POSIX',
     ]
+elif system.startswith('CYGWIN'):
+    extra_compile_args = common_flags + [
+        '-lpthread',
+        '-Wall',
+        '-DOS_LINUX',
+        '-DLEVELDB_PLATFORM_POSIX',
+        '-DCYGWIN',
+    ]
 else:
     sys.stderr.write("Don't know how to compile leveldb for %s!\n" % system)
     sys.exit(1)
$

I wonder if we can add this feature.