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.
Teach the CDASH_UPLOAD signature of ctest_submit() to honor the
RETRY_COUNT and RETRY_DELAY options.
Also teach HttpRequest() to honor the default 120 second timeout
for curl connections.
A more-specific error message is always displayed earlier in the
output if any real error occurred. This final summary message
is distracting to readers searching through the output for the
word "error". Simply drop it.
Zack Galbreath