Merge branch 'jk/dev-build-format-security'

Merge branch 'jk/dev-build-format-security'

Earlier we added "-Wformat-security" to developer builds, assuming
that "-Wall" (which includes "-Wformat" which in turn is required
to use "-Wformat-security") is always in effect.  This is not true
when config.mak.autogen is in use, unfortunately.  This has been
fixed by unconditionally adding "-Wall" to developer builds.

* jk/dev-build-format-security:
  config.mak.dev: add -Wall, primarily for -Wformat, to help autoconf users