Help: Clarify `ctest_*` APPEND option behavior

Explicitly state that this marks the `.xml` to tell the dashboard
server to append it to previously submitted results and that it
does not cause results to be appended to the `.xml` file.

Help/command/ctest_build.rst

@@ -30,9 +30,11 @@ The options are:
   :variable:`CTEST_BINARY_DIRECTORY` variable is used.
 
 ``APPEND``
-  Mark results for append to those previously submitted to a
+  Mark ``Build.xml`` for append to results previously submitted to a
   dashboard server since the last :command:`ctest_start` call.
   Append semantics are defined by the dashboard server in use.
+  This does *not* cause results to be appended to a ``.xml`` file
+  produced by a previous call to this command.
 
 ``CONFIGURATION <config>``
   Specify the build configuration (e.g. ``Debug``).  If not

Help/command/ctest_configure.rst

@@ -23,9 +23,11 @@ The options are:
   :variable:`CTEST_SOURCE_DIRECTORY` variable is used.
 
 ``APPEND``
-  Mark results for append to those previously submitted to a
+  Mark ``Configure.xml`` for append to results previously submitted to a
   dashboard server since the last :command:`ctest_start` call.
   Append semantics are defined by the dashboard server in use.
+  This does *not* cause results to be appended to a ``.xml`` file
+  produced by a previous call to this command.
 
 ``OPTIONS <options>``
   Specify command-line arguments to pass to the configuration tool.

Help/command/ctest_coverage.rst

@@ -22,9 +22,11 @@ The options are:
   :variable:`CTEST_BINARY_DIRECTORY` variable is used.
 
 ``APPEND``
-  Mark results for append to those previously submitted to a
+  Mark ``Coverage.xml`` for append to results previously submitted to a
   dashboard server since the last :command:`ctest_start` call.
   Append semantics are defined by the dashboard server in use.
+  This does *not* cause results to be appended to a ``.xml`` file
+  produced by a previous call to this command.
 
 ``LABELS``
   Filter the coverage report to include only source files labeled

Help/command/ctest_test.rst

@@ -32,9 +32,11 @@ The options are:
   :variable:`CTEST_BINARY_DIRECTORY` variable is used.
 
 ``APPEND``
-  Mark results for append to those previously submitted to a
+  Mark ``Test.xml`` for append to results previously submitted to a
   dashboard server since the last :command:`ctest_start` call.
   Append semantics are defined by the dashboard server in use.
+  This does *not* cause results to be appended to a ``.xml`` file
+  produced by a previous call to this command.
 
 ``START <start-number>``
   Specify the beginning of a range of test numbers.