Upgrade to coverage 3.7.1 and have it auto-build itself on first use.

third_party/coverage-3.7.1/doc/cmd.rst

Index: third_party/coverage-3.7.1/doc/cmd.rst
diff --git a/third_party/coverage-3.6/doc/cmd.rst b/third_party/coverage-3.7.1/doc/cmd.rst
similarity index 92%
rename from third_party/coverage-3.6/doc/cmd.rst
rename to third_party/coverage-3.7.1/doc/cmd.rst
index 6b1d15dc65b6c721d83e73305a789efe18fd41fe..49062b31db1deacf0c163ed5e945e07f076092f9 100644
--- a/third_party/coverage-3.6/doc/cmd.rst
+++ b/third_party/coverage-3.7.1/doc/cmd.rst
@@ -138,6 +138,24 @@ could affect the measurement process.  The possible warnings include:
   This could be because you asked to measure only modules that never ran,
   or for other reasons.
 
+.. _cmd_run_debug:
+
+The ``--debug`` option instructs coverage to log internal details of its
+operation, to help with diagnosing problems.  It takes a comma-separated list
+of options, each indicating a facet of operation to log to stderr:
+
+* ``trace``: print every decision about whether to trace a file or not. For
+  files not being traced, the reason is also given.
+
+* ``config``: before starting, dump all the :ref:`configuration <config>`
+  values.
+
+* ``sys``: before starting, dump all the system and environment information,
+  as with :ref:`coverage debug sys <cmd_debug>`.
+
+* ``dataio``: log when reading or writing any data file.
+
+* ``pid``: annotate all debug output with the process id.
 
 
 .. _cmd_datafile:
@@ -168,9 +186,9 @@ coverage can combine multiple files into one for reporting. Use the ``-p`` flag
 during execution to append distinguishing information to the .coverage data
 file name.
 
-Once you have created a number of these files, you can copy them all to a single
-directory, and use the **combine** command to combine them into one .coverage
-data file::
+Once you have created a number of these files, you can copy them all to a
+single directory, and use the **combine** command to combine them into one
+.coverage data file::
 
     $ coverage combine
 
@@ -308,10 +326,10 @@ generating unchanged pages, making the process faster.
 Text annotation
 ---------------
 
-The **annotate** command produces a text annotation of your source code.  With a
-``-d`` argument specifying an output directory, each Python file becomes a text
-file in that directory.  Without ``-d``, the files are written into the same
-directories as the original Python files.
+The **annotate** command produces a text annotation of your source code.  With
+a ``-d`` argument specifying an output directory, each Python file becomes a
+text file in that directory.  Without ``-d``, the files are written into the
+same directories as the original Python files.
 
 Coverage status for each line of source is indicated with a character prefix::