configure: Let the user enable both built-in protocols and purple

There's no real risk in enabling these, since protocols/purple/purple.c
already avoids adding duplicate protocols in purple_initmodule():

    /* If we already have this one (as a native module), don't
       add a libpurple duplicate. */
    if( find_protocol( prot->info->id ) )
        continue;
Gadugadu local contact storage (ticket #917)

Patch originally by Michał Siejak, adapted for 3.2.1
Merge branch 'patch/purple-protocol-override-dx' into develop
Fix double slashes in systemd unit templates
Travis CI integration
Travis: Speed up build by using --no-install-recommends
Fix srv_lookup issues on cygwin (and other platforms)

The srv_lookup routine in lib/misc.c always returns zero responses on
Cygwin. It is configured to do this because the ns_initparse and
ns_parserr routines are not provided on Cygwin. Because srv_lookup
always returns zero results Jabber accounts where the server does not
match the @server.com portion of the username have to explicitly set a
server name. This means that you can not do tls_verify on those
accounts. For instance, username@gmail.com with a srv_lookup fail must
set server name to talk.google.com. But Google returns a certificate for
gmail.com which the verify code thinks is the wrong server because it
does not match the server name.

This patch does 3 things.

1. It changes the configure script to check for res_qeruy and
dn_expandname when looking for libresolv. It also has a new check for
ns_initparse and ns_initparserr to see if libresolv or libc provides
them.

2. It changes the lib/misc.c srv_lookup routine to use dn_expandname
instead of the custom code. This allows srv_lookup to process compressed
names correctly. Cygwin res_query returns a compressed name and since
bitlbee already requires libresolv this seems like the more correct
solution.

3. It adds lib/ns_parse.c to provide ns_initparse and ns_parserr on
platforms where those were not detected at ./configure time. This is a
copy of a file from libbind-6.0 source with the copyright still in place
and just minor modification. Removal of two functions that bitlbee does
not use and added some #ifdefds and #include “bittlbee.h”. Reading the
copyright/license notice I believe this is acceptable.

The end goal of this patch is to allow me to set up a Jabber account
with username@gmail.com and tls_verify to true.
srv_lookup: Detect missing types and add custom definitions if not there