setup: switch to with open as

We're leaving the modulepolicy bit alone, because it's being
rewritten in the next commit.

setup.py

@@ -207,11 +207,9 b" elif os.path.exists('.hg_archival.txt'):"
         version = kw.get('node', '')[:12]
 
 if version:
-    f = open("mercurial/__version__.py", "w")
+    with open("mercurial/__version__.py", "w") as f:
     f.write('# this file is autogenerated by setup.py\n')
     f.write('version = "%s"\n' % version)
-    f.close()
-
 
 try:
     from mercurial import __version__
@@ -345,9 +343,8 b' class buildhgextindex(Command):'
 
     def run(self):
         if os.path.exists(self._indexfilename):
-            f = open(self._indexfilename, 'w')
+            with open(self._indexfilename, 'w') as f:
             f.write('# empty\n')
-            f.close()
 
         # here no extension enabled, disabled() lists up everything
         code = ('import pprint; from mercurial import extensions; '
@@ -356,11 +353,10 b' class buildhgextindex(Command):'
         if err:
             raise DistutilsExecError(err)
 
-        f = open(self._indexfilename, 'w')
+        with open(self._indexfilename, 'w') as f:
         f.write('# this file is autogenerated by setup.py\n')
         f.write('docs = ')
         f.write(out)
-        f.close()
 
 class buildhgexe(build_ext):
     description = 'compile hg.exe from mercurial/exewrapper.c'
@@ -373,10 +369,9 b' class buildhgexe(build_ext):'
             self.compiler.dll_libraries = [] # no -lmsrvc90
         hv = sys.hexversion
         pythonlib = 'python%d%d' % (hv >> 24, (hv >> 16) & 0xff)
-        f = open('mercurial/hgpythonlib.h', 'wb')
+        with open('mercurial/hgpythonlib.h', 'wb') as f:
         f.write('/* this file is autogenerated by setup.py */\n')
         f.write('#define HGPYTHONLIB "%s"\n' % pythonlib)
-        f.close()
         objects = self.compiler.compile(['mercurial/exewrapper.c'],
                                          output_dir=self.build_temp)
         dir = os.path.dirname(self.get_ext_fullpath('dummy'))
@@ -476,9 +471,8 b' class hginstallscripts(install_scripts):'
             libdir = uplevel * ('..' + os.sep) + self.install_lib[len(common):]
 
         for outfile in self.outfiles:
-            fp = open(outfile, 'rb')
+            with open(outfile, 'rb') as fp:
             data = fp.read()
-            fp.close()
 
             # skip binary files
             if b'\0' in data:
@@ -493,9 +487,8 b' class hginstallscripts(install_scripts):'
                 continue
 
             data = data.replace(b'@LIBDIR@', libdir.encode(libdir_escape))
-            fp = open(outfile, 'wb')
+            with open(outfile, 'wb') as fp:
             fp.write(data)
-            fp.close()
 
 cmdclass = {'build': hgbuild,
             'build_mo': hgbuildmo,