tests: open file in binary mode to use POSIX end-of-line style anywhere

Before this patch, "test-context.py" fails on Windows environment,
because "diff" output contains unexpected "\r" character.

Opening the target file in text mode causes this automatic end-of-line
conversion.

tests/test-context.py

@@ -1,52 +1,52 b''
 import os
 from mercurial import hg, ui, context, encoding
 
 u = ui.ui()
 
 repo = hg.repository(u, 'test1', create=1)
 os.chdir('test1')
 
 # create 'foo' with fixed time stamp
-f = open('foo', 'w')
+f = open('foo', 'wb')
 f.write('foo\n')
 f.close()
 os.utime('foo', (1000, 1000))
 
 # add+commit 'foo'
 repo[None].add(['foo'])
 repo.commit(text='commit1', date="0 0")
 
 print "workingfilectx.date =", repo[None]['foo'].date()
 
 # test memctx with non-ASCII commit message
 
 def filectxfn(repo, memctx, path):
     return context.memfilectx(repo, "foo", "")
 
 ctx = context.memctx(repo, ['tip', None],
                      encoding.tolocal("Gr\xc3\xbcezi!"),
                      ["foo"], filectxfn)
 ctx.commit()
 for enc in "ASCII", "Latin-1", "UTF-8":
     encoding.encoding = enc
     print "%-8s: %s" % (enc, repo["tip"].description())
 
 # test performing a status
 
 def getfilectx(repo, memctx, f):
     fctx = memctx.parents()[0][f]
     data, flags = fctx.data(), fctx.flags()
     if f == 'foo':
         data += 'bar\n'
     return context.memfilectx(repo, f, data, 'l' in flags, 'x' in flags)
 
 ctxa = repo.changectx(0)
 ctxb = context.memctx(repo, [ctxa.node(), None], "test diff", ["foo"],
                       getfilectx, ctxa.user(), ctxa.date())
 
 print ctxb.status(ctxa)
 
 # test performing a diff on a memctx
 
 for d in ctxb.diff(ctxa, git=True):
     print d