issue2551203 - Add support for CORS preflight request Add support for unauthenticated CORS preflight and fix headers for CORS. client.py: pass through unauthenticated CORS preflight to rest backend. Normal rest OPTION handlers (including tracker defined extensions) can see and handle the request. make some error cases return error json with crrect mime type rather than plain text tracebacks. create new functions to verify origin and referer that filter using allowed origins setting. remove tracker base url from error message is referer is not at an allowed origin. rest.py: fix up OPTION methods handlers to include Access-Control-Allow-Methods that are the same as the Allow header. set cache to one week for all Access-Control headers for CORS preflight only. remove self.client.setHeader("Access-Control-Allow-Origin", "*") and set Access-Control-Allow-Origin to the client supplied origin if it passes allowed origin checks. Required for CORS otherwise data isn't available to caller. Set for all responses. set Vary header now includes Origin as responses can differ based on Origin for all responses. set Access-Control-Allow-Credentials to true on all responses. test_liveserver.py: run server with setting to enforce origin csrf header check run server with setting to enforce x-requested-with csrf header check run server with setting for allowed_api_origins requests now set required csrf headers test preflight request on collections check new headers and Origin is no longer '*' rewrite all compression checks to use a single method with argument to use different compression methods. Reduce a lot of code duplication and makes updating for new headers easier. test_cgi: test new error messages in client.py account for new headers test preflight and new code paths

A number of tests uses the infrastructure of
	db_test_base.py

grep "from db_test_base" -l *.py
benchmark.py
session_common.py
test_anydbm.py
test_indexer.py
test_memorydb.py
test_mysql.py
test_postgresql.py
test_security.py
test_sqlite.py
test_userauditor.py

grep "import db_test_base" -l *.py
test_cgi.py
test_jinja2.py
test_mailgw.py
test_xmlrpc.py

grep "import memory\|from memory" -l *.py 
test_mailgw.py
test_memorydb.py


The remaining lines are an 2001 description from Richard,
which probably is outdated:

Structure of the tests:

   1   Test date classes
   1.1 Date
   1.2 Interval
   2   Set up schema
   3   Open with specific backend
   3.1 anydbm
   4   Create database base set (stati, priority, etc)
   5   Perform some actions
   6   Perform mail import
   6.1 text/plain
   6.2 multipart/mixed (with one text/plain)
   6.3 text/html
   6.4 multipart/alternative (with one text/plain)
   6.5 multipart/alternative (with no text/plain)