profiling: flush stdout before writing profile to stderr

On py3, stdout and stderr appear to be buffered and this causes my command's
output to be intermixed with the profiling output.

Differential Revision: https://phab.mercurial-scm.org/D8024

mercurial/profiling.py

@@ -186,6 +186,7 b' class profile(object):'
         self._output = None
         self._fp = None
         self._fpdoclose = True
+        self._flushfp = None
         self._profiler = None
         self._enabled = enabled
         self._entered = False
@@ -246,6 +247,8 b' class profile(object):'
             else:
                 self._fpdoclose = False
                 self._fp = self._ui.ferr
+                # Ensure we've flushed fout before writing to ferr.
+                self._flushfp = self._ui.fout
 
             if proffn is not None:
                 pass
@@ -265,6 +268,7 b' class profile(object):'
     def __exit__(self, exception_type, exception_value, traceback):
         propagate = None
         if self._profiler is not None:
+            self._uiflush()
             propagate = self._profiler.__exit__(
                 exception_type, exception_value, traceback
             )
@@ -280,3 +284,7 b' class profile(object):'
     def _closefp(self):
         if self._fpdoclose and self._fp is not None:
             self._fp.close()
+
+    def _uiflush(self):
+        if self._flushfp:
+            self._flushfp.flush()