help: fix typo in hg merge documentation

mercurial/filemerge.py

@@ -459,7 +459,7 b' def _idump(repo, mynode, orig, fcd, fco,'
     ``a.txt.other`` and ``a.txt.base`` and they will be placed in the
     same directory as ``a.txt``.
 
-    This implies permerge. Therefore, files aren't dumped, if premerge
+    This implies premerge. Therefore, files aren't dumped, if premerge
     runs successfully. Use :forcedump to forcibly write files out.
     """
     a = _workingpath(repo, fcd)

tests/test-help.t

@@ -1792,7 +1792,7 b' Test dynamic list of merge tools only sh'
         accordingly be named "a.txt.local", "a.txt.other" and "a.txt.base" and
         they will be placed in the same directory as "a.txt".
   
-        This implies permerge. Therefore, files aren't dumped, if premerge runs
+        This implies premerge. Therefore, files aren't dumped, if premerge runs
         successfully. Use :forcedump to forcibly write files out.
   
       ":fail"