Also, stop implying that Roger still does all the source releases.

Document this convention.

Add a script to post-process .gcov files in order to stop nagging us
about excluded lines.

Teach cov-diff to handle these post-processed files.

Closes ticket 16792

Closes #17839.

Not good markdown, mind you.

Document use of coverity, clang static analyzer, and clang dynamic
undefined behavior and address sanitizers in doc/HACKING.

Add clang dynamic sanitizer blacklist in
contrib/clang/sanitizer_blacklist.txt to exempt known undefined
behavior. Include detailed usage instructions in this blacklist file.

Patch by "teor".