chgserver: update the umask cache before each run

chgserver: update the umask cache before each run

posix.py uses a global variable to store the umask value resulting in caching of
it when using chg. We need to update it before each command run as the umask can
change between commands.

This fixes test-inherit-mode.t with chg.

--- a/mercurial/chgserver.py	Thu Mar 26 10:09:17 2020 -0400
+++ b/mercurial/chgserver.py	Tue Mar 31 15:11:33 2020 +0530
@@ -528,7 +528,7 @@
     def _setumask(self, data):
         mask = struct.unpack(b'>I', data)[0]
         self.ui.log(b'chgserver', b'setumask %r\n', mask)
-        os.umask(mask)
+        util.setumask(mask)
 
     def runcommand(self):
         # pager may be attached within the runcommand session, which should

--- a/mercurial/util.py	Thu Mar 26 10:09:17 2020 -0400
+++ b/mercurial/util.py	Tue Mar 31 15:11:33 2020 +0530
@@ -130,6 +130,16 @@
 unlink = platform.unlink
 username = platform.username
 
+
+def setumask(val):
+    ''' updates the umask. used by chg server '''
+    if pycompat.iswindows:
+        return
+    os.umask(val)
+    global umask
+    platform.umask = umask = val & 0o777
+
+
 # small compat layer
 compengines = compression.compengines
 SERVERROLE = compression.SERVERROLE