ctest_submit: Add HTTPHEADER option

Allow CTest script writers to specify additional HTTP headers to be sent
to CDash during submission.

The motivating case for this feature is a corresponding change in CDash.
This will allow projects to refuse submissions from any site not bearing
a valid authentication token.

Help/command/ctest_submit.rst

@@ -6,6 +6,7 @@ Perform the :ref:`CTest Submit Step` as a :ref:`Dashboard Client`.
 ::
 
   ctest_submit([PARTS <part>...] [FILES <file>...]
+               [HTTPHEADER <header>]
                [RETRY_COUNT <count>]
                [RETRY_DELAY <delay>]
                [RETURN_VALUE <result-var>]
@@ -36,6 +37,10 @@ The options are:
   Specify an explicit list of specific files to be submitted.
   Each individual file must exist at the time of the call.
 
+``HTTPHEADER <HTTP-header>``
+  Specify HTTP header to be included in the request to CDash during submission.
+  This suboption can be repeated several times.
+
 ``RETRY_COUNT <count>``
   Specify how many times to retry a timed-out submission.
 
@@ -57,6 +62,7 @@ Submit to CDash Upload API
 ::
 
   ctest_submit(CDASH_UPLOAD <file> [CDASH_UPLOAD_TYPE <type>]
+               [HTTPHEADER <header>]
                [RETRY_COUNT <count>]
                [RETRY_DELAY <delay>]
                [QUIET])
@@ -67,5 +73,5 @@ with a content hash of the file. If CDash does not already have the file,
 then it is uploaded. Along with the file, a CDash type string is specified
 to tell CDash which handler to use to process the data.
 
-This signature accepts the ``RETRY_COUNT``, ``RETRY_DELAY``, and ``QUIET``
-options as described above.
+This signature accepts the ``HTTPHEADER``, ``RETRY_COUNT``, ``RETRY_DELAY``, and
+``QUIET`` options as described above.