py3: conditionalize the raise statement

raise E,V,T is not acceptable in Python 3, thats is conditionalized.
Moreover this will result in syntax error so we have to use exec() to
execute this. Related PEP- https://www.python.org/dev/peps/pep-3109/#id14

My implementation is motivated from the six implementation except they are
defining a new function exec_() to prevent adding an extra frame AFAIK :)

https://bitbucket.org/gutworth/six/src/ca4580a5a648/six.py#six.py-680

mercurial/bundle2.py

@@ -989,7 +989,10 b' class bundlepart(object):'
             outdebug(ui, 'closing payload chunk')
             # abort current part payload
             yield _pack(_fpayloadsize, 0)
-            raise exc_info[0], exc_info[1], exc_info[2]
+            if sys.version_info[0] >= 3:
+                raise exc_info[0](exc_info[1]).with_traceback(exc_info[2])
+            else:
+                exec("""raise exc_info[0], exc_info[1], exc_info[2]""")
         # end of payload
         outdebug(ui, 'closing payload chunk')
         yield _pack(_fpayloadsize, 0)

tests/test-check-py3-compat.t

@@ -81,7 +81,7 b''
   mercurial/archival.py: invalid syntax: invalid syntax (<unknown>, line *) (glob)
   mercurial/bookmarks.py: error importing: <TypeError> str expected, not bytes (error at encoding.py:*) (glob)
   mercurial/branchmap.py: error importing: <TypeError> str expected, not bytes (error at encoding.py:*) (glob)
-  mercurial/bundle2.py: invalid syntax: invalid syntax (<unknown>, line *) (glob)
+  mercurial/bundle2.py: error importing: <TypeError> str expected, not bytes (error at encoding.py:*) (glob)
   mercurial/bundlerepo.py: error importing: <TypeError> str expected, not bytes (error at encoding.py:*) (glob)
   mercurial/byterange.py: error importing: <TypeError> str expected, not bytes (error at encoding.py:*) (glob)
   mercurial/changegroup.py: error importing: <TypeError> str expected, not bytes (error at encoding.py:*) (glob)
@@ -141,7 +141,7 b''
   mercurial/pushkey.py: error importing: <TypeError> getattr(): attribute name must be string (error at pycompat.py:*) (glob)
   mercurial/pvec.py: error importing: <TypeError> getattr(): attribute name must be string (error at pycompat.py:*) (glob)
   mercurial/registrar.py: error importing: <TypeError> getattr(): attribute name must be string (error at util.py:*) (glob)
-  mercurial/repair.py: error importing module: <SyntaxError> invalid syntax (bundle2.py, line *) (line *) (glob)
+  mercurial/repair.py: error importing: <TypeError> getattr(): attribute name must be string (error at util.py:*) (glob)
   mercurial/repoview.py: error importing: <TypeError> getattr(): attribute name must be string (error at util.py:*) (glob)
   mercurial/revlog.py: error importing: <TypeError> getattr(): attribute name must be string (error at util.py:*) (glob)
   mercurial/revset.py: error importing: <TypeError> getattr(): attribute name must be string (error at util.py:*) (glob)
@@ -168,6 +168,6 b''
   mercurial/verify.py: error importing: <TypeError> attribute name must be string, not 'bytes' (error at mdiff.py:*) (glob)
   mercurial/win32.py: error importing module: <ImportError> No module named 'msvcrt' (line *) (glob)
   mercurial/windows.py: error importing module: <ImportError> No module named '_winreg' (line *) (glob)
-  mercurial/wireproto.py: error importing module: <SyntaxError> invalid syntax (bundle2.py, line *) (line *) (glob)
+  mercurial/wireproto.py: error importing module: <TypeError> a bytes-like object is required, not 'str' (line *) (glob)
 
 #endif