hgweb: discard Content-Type header for 304 responses (issue5844) A side-effect of 98baf8dea553 was that hgwebdir always sets a global default for the Content-Type header. HTTP 304 responses don't allow the Content-Type header. So a side-effect of this change was that HTTP 304 responses served via hgwebdir resulted in a ProgrammingError being raised. This commit teaches our 304 response issuing code to drop the Content-Type header. Differential Revision: https://phab.mercurial-scm.org/D3435

tests: add tests demonstrating ISE for HTTP 304 responses with hgwebdir There are two separate failures here. One for the Content-Type header. Another for the Content-Security-Policy header. Differential Revision: https://phab.mercurial-scm.org/D3434