Fold new entries into 0.2.5.7 changelog

changes/bug12878

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-  o Documentation:
-    - Document 'reject6' and 'accept6' ExitPolicy entries. Resolves 
-      ticket 12878.

changes/bug12948

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-  o Major bugfixes:
-    - Resume expanding abbreviations for command-line options. The fix
-      for bug 4647 accidentally removed our hack from bug 586 that rewrote
-      HashedControlPassword to __HashedControlSessionPassword when it
-      appears on the commandline (which allowed the user to set her
-      own HashedControlPassword in the torrc file while the controller
-      generates a fresh session password for each run). Fixes bug 12948;
-      bugfix on 0.2.5.1-alpha.

changes/bug12996

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-  o Minor bugfixes:
-    - Downgrade "Unexpected onionskin length after decryption" warning
-      to a protocol-warn, since there's nothing relay operators can do
-      about a client that sends them a malformed create cell. Resolves
-      bug 12996; bugfix on 0.0.6rc1.

changes/bug12997

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-  o Minor features:
-    - Log more specific warnings when we get an ESTABLISH_RENDEZVOUS cell
-      on a cannibalized or non-OR circuit. Resolves ticket 12997.

changes/ticket13036

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-  o Minor bugfixes:
-    - Fix a large number of false positive warnings from the clang
-      analyzer static analysis tool. This should make real warnings
-      easier for clang analyzer to find. Patch from "teor". Closes
-      ticket 13036.