profiling: move 'fp' closing logic into its own function

We are about to make the logic more robust and reuse it in more place, we start
by isolating what we have.

mercurial/profiling.py

@@ -218,4 +218,7 b' class profile(object):'
                 # so we need to escape any % signs.
                 val = val.replace('%', '%%')
                 self._ui.log('profile', val)
-            self._fp.close()
+            self._closefp()
+
+    def _closefp(self):
+        self._fp.close()