WEBIRC: Don't respect hostname when DNS is disabled

When DNS lookups are disabled, don't set the hostname received by the
WEBIRC command, but use the IP address instead.

Reported by Toni Spets <toni.spets@iki.fi>, thanks!

Closes bug #167.
Implement new configuration option "Network"

The new configuration variable "Network" is used to set the (completely
optional) "network name", to which this instance of the daemon belongs.
When set, this name is used in the ISUPPORT(005) numeric which is sent to
all clients connecting to the server after logging in.

Closes bug #165.
portabtest: Code cleanup
portabtest: Only use one exit code to indicate errors
portabtest: Actually test functions

Test functions snprintf(), strlcpy(), strlcat(), vsnprintf() for
correctness, not only existance (which was quite useless, because
if they weren't available, the program could not have been linked
at all ...).
portabtest: Add checks for strdup(), strndup(), and strtok_r()
Merge branch 'bug165-005-NETWORK' of git://arthur.barton.de/ngircd-alex

* 'bug165-005-NETWORK' of git://arthur.barton.de/ngircd-alex:
  Implement new configuration option "Network"
Merge branch 'bug167-WebircIPAnoDNS' of git://arthur.barton.de/ngircd-alex

* 'bug167-WebircIPAnoDNS' of git://arthur.barton.de/ngircd-alex:
  WEBIRC: Don't respect hostname when DNS is disabled
Update Copyright notices for 2014
Update configure.ng for autoconf 2.67

We already require GNU autoconf 2.67 for generating our build system (at
least this is what the INSTALL document states), so update the build system
accordingly and implement all changes that autoupdate(1) suggests:

 - Update AC_PREREQ and AC_INIT
 - Use AC_LINK_IFELSE, AC_RUN_IFELSE, and AC_COMPILE_IFELSE
 - Remove AC_TYPE_SIGNAL (we don't use RETSIGTYPE)
doc/Platforms.txt: Update some systems to ngIRCd 21

- update i686/pc/cygwin, gcc 4.8.2
- update x86_64/apple/darwin13.0.0, Apple clang 5.0
- update x86_64/unknown/freebsd8.4, gcc 4.2.1
- update x86_64/unknown/freebsd9.1, gcc 4.2.1
- update x86_64/unknown/linux-gnu, gcc 4.8.2
- update x86_64/unknown/linux-gnu, Open64
- update x86_64/unknown/openbsd4.8, gcc 4.2.1
- update x86_64/unknown/openbsd5.1, gcc 4.2.1
Partially revert bc098794: don't require autoconf 2.67

GNU autoconf 2.61 is still sufficient to generate the configure script, even
after updating configure.{ng|in}, so don't require a newer version.
Support non-standard vsnprintf() return code

C99 states that vsnprintf() "returns the number of characters that
would have been printed if the n were unlimited"; but according to the
Linux manual page "glibc until 2.0.6 would return -1 when the output
was truncated" -- so we have to handle both cases ...
Makefile.am: don't use "test -e", it isn't portable
platformtest.sh: don't use "test -e", it isn't portable
Add "config.cache" to .gitignore file