commands: print chunk type in debugrevlog Each data entry ("chunk") in a revlog has a type based on the first byte of the data. This type indicates how to interpret the data. This seems like a useful thing to be able to query through a debug command. So let's add that to `hg debugrevlog`. This does make `hg debugrevlog` slightly slower, as it has to read more than just the index. However, even on the mozilla-unified manifest (which is ~200MB spread over ~350K revisions), this takes <400ms.

--- a/tests/test-debugcommands.t	Thu Nov 17 20:17:51 2016 -0800
+++ b/tests/test-debugcommands.t	Thu Nov 17 20:30:00 2016 -0800
@@ -22,6 +22,11 @@
       full      : 44 (100.00%)
       deltas    :  0 ( 0.00%)
   
+  chunks        :  1
+      0x75 (u)  :  1 (100.00%)
+  chunks size   : 44
+      0x75 (u)  : 44 (100.00%)
+  
   avg chain length  : 0
   max chain length  : 0
   compression ratio : 0