mitogen: Golf 8 bytes from bootstrap first stage (798 -> 790)

Before
```
SSH command size: 798
Preamble (mitogen.core + econtext) size: 18230 (17.80KiB)

                        Original           Minimized           Compressed
mitogen.core         152237 148.7KiB  68453 66.8KiB 45.0%  18130 17.7KiB 11.9%
mitogen.parent        99020  96.7KiB  51247 50.0KiB 51.8%  12910 12.6KiB 13.0%
mitogen.fork           8445   8.2KiB   4139  4.0KiB 49.0%   1652  1.6KiB 19.6%
mitogen.ssh           10847  10.6KiB   6913  6.8KiB 63.7%   2102  2.1KiB 19.4%
mitogen.sudo          12089  11.8KiB   5924  5.8KiB 49.0%   2249  2.2KiB 18.6%
mitogen.select        12325  12.0KiB   2929  2.9KiB 23.8%    964  0.9KiB  7.8%
mitogen.service       41581  40.6KiB  22398 21.9KiB 53.9%   5847  5.7KiB 14.1%
mitogen.fakessh       15753  15.4KiB   8135  7.9KiB 51.6%   2672  2.6KiB 17.0%
mitogen.master        52891  51.7KiB  27586 26.9KiB 52.2%   7129  7.0KiB 13.5%
```

After
```
SSH command size: 790
Preamble (mitogen.core + econtext) size: 18230 (17.80KiB)

                        Original           Minimized           Compressed
mitogen.core         152237 148.7KiB  68453 66.8KiB 45.0%  18130 17.7KiB 11.9%
mitogen.parent        99020  96.7KiB  51247 50.0KiB 51.8%  12903 12.6KiB 13.0%
mitogen.fork           8445   8.2KiB   4139  4.0KiB 49.0%   1652  1.6KiB 19.6%
mitogen.ssh           10847  10.6KiB   6913  6.8KiB 63.7%   2102  2.1KiB 19.4%
mitogen.sudo          12089  11.8KiB   5924  5.8KiB 49.0%   2249  2.2KiB 18.6%
mitogen.select        12325  12.0KiB   2929  2.9KiB 23.8%    964  0.9KiB  7.8%
mitogen.service       41581  40.6KiB  22398 21.9KiB 53.9%   5847  5.7KiB 14.1%
mitogen.fakessh       15753  15.4KiB   8135  7.9KiB 51.6%   2672  2.6KiB 17.0%
mitogen.master        52891  51.7KiB  27586 26.9KiB 52.2%   7129  7.0KiB 13.5%
```

mitogen/parent.py

@@ -1435,20 +1435,21 @@ class Connection(object):
             os.close(r)
             os.close(W)
             os.close(w)
-            if os.uname()[0]=='Darwin'and os.uname()[2][:2]<'19'and sys.executable=='/usr/bin/python':sys.executable='/usr/bin/python2.7'
+            if os.uname()[0]+os.uname()[2][:2]+sys.executable=='Darwin19/usr/bin/python':sys.executable+='2.7'
-            if os.uname()[0]=='Darwin'and os.uname()[2][:2]in'2021'and sys.version[:3]=='2.7':os.environ['PYTHON_LAUNCHED_FROM_WRAPPER']='1'
+            if os.uname()[0]+os.uname()[2][:2]+sys.version[:3]=='Darwin202.7':os.environ['PYTHON_LAUNCHED_FROM_WRAPPER']='1'
+            if os.uname()[0]+os.uname()[2][:2]+sys.version[:3]=='Darwin212.7':os.environ['PYTHON_LAUNCHED_FROM_WRAPPER']='1'
             os.environ['ARGV0']=sys.executable
             os.execl(sys.executable,sys.executable+'(mitogen:CONTEXT_NAME)')
         os.write(1,'MITO000\n'.encode())
         C=''.encode()
         while PREAMBLE_COMPRESSED_LEN-len(C)and select.select([0],[],[]):C+=os.read(0,PREAMBLE_COMPRESSED_LEN-len(C))
         C=zlib.decompress(C)
-        fp=os.fdopen(W,'wb',0)
+        f=os.fdopen(W,'wb',0)
-        fp.write(C)
+        f.write(C)
-        fp.close()
+        f.close()
-        fp=os.fdopen(w,'wb',0)
+        f=os.fdopen(w,'wb',0)
-        fp.write(C)
+        f.write(C)
-        fp.close()
+        f.close()
         os.write(1,'MITO001\n'.encode())
         os.close(2)