Add optional [FILE] argument to all agents reading policy

This is an alternative to specifying input file via -f.
e.g. cf-promises file.cf resolves to cf-promises -f ./test.cf

Close #2303
Make --help option have more standard output
Remove CPPFLAGS manipulation from configure.ac

it was erroneous anyway since it was adding an object (not source) directory.
Separate existing networking code, create libcfnet directory

...the beginning of a new era?
Move more stuff to libcfnet, get rid of some thread-unsafe code

* Move AgentConnection to libcfnet, which caused inclusion of cfnet.h from
  many files.

* Remove cf3.defs.h dependency from most of libcfnet, move network specific
  defines to cfnet.h.

* Remove most of sockaddr.c and replace the thread-unsafe sockaddr_{pton,ntop}
  functions with inet_{pton,ntop} from POSIX, or getnameinfo(NI_NUMERICHOST)
  when HAVE_GETADDRINFO is valid. Needed functionality was retained in
  libcfnet/misc.c, to be removed.

* Detect missing declarations of inet_ntop(), inet_pton() through autoconf and
  provide replacements if needed. For replacements, implementation used is
  copyright ISC and flexibly licensed.
Remove old commented code
Use getaddrinfo and friends whenever possible

* Remove lots of old hidden #ifdef !HAVE_GETADDRINFO code that barely run
  anywhere, and use getaddrinfo whenever possible.

* Provide replacement functions in libcompat (Copyright PostgreSQL, freely
  licensed) for legacy platforms.

* Use getnameinfo(NI_NUMERICHOST) to convert IP address to string in a
  IP-version agnostic manner.
Add copyright blurb
Revert "Adopt a defensive tokyo cabinet strategy. Before opening a cursor make sur the store is coherent"

This reverts commit 4fa7754bb8f944c299dd683c271942cf8f6f64d7.
Merge remote branch 'upstream/master'