http: add debug message for invalid header value
Checklist
-
make -j8 test
(UNIX), orvcbuild test nosign
(Windows) passes -
commit message follows commit guidelines
Affected core subsystem(s)
http
Description of change
This makes it easier to see what header has an invalid value. As discussed on the CTC call today (10/19/2016), this is a way to get which header is causing the throw without introducing a breaking change (changing error messages is considered breaking)