lprng: FTBFS on Natty because of pickier linker

Binary package hint: lprng

On Ubuntu Natty, the lprng source package fails to build with the following error:

gcc -g -O2 -Wl,-Bsymbolic-functions -o lpr lpr.o openprinter.o stty.o child.o copyright.o debug.o errormsg.o fileopen.o gethostinfo.o getopt.o getprinter.o getqueue.o globmatch.o initialize.o krb5_auth.o linelist.o linksupport.o lockfile.o merge.o plp_snprintf.o printjob.o proctitle.o sendjob.o sendauth.o sendreq.o ssl_auth.o user_auth.o utilities.o vars.o md5.o -lkrb5 -lcrypto -lcom_err
/usr/bin/ld: krb5_auth.o: undefined reference to symbol 'krb5_encrypt_size@@k5crypto_3_MIT'
/usr/bin/ld: note: 'krb5_encrypt_size@@k5crypto_3_MIT' is defined in DSO /usr/lib/libk5crypto.so.3 so try adding it to the linker command line
/usr/lib/libk5crypto.so.3: could not read symbols: Invalid operation
collect2: ld returned 1 exit status
make[3]: *** [lpr] Error 1

As indicated by the error, the issue is that -lk5crypto is not being passed. It turns out that configure.ac isn't using krb5-config, which is the standard way to figure out what the linker flags should be. This seems to have been fine in previous releases (and this version of the package was never rebuilt since being imported from Debian), but Natty's toolchain is not happy with this.

I'm attaching a debdiff that adds a few lines to configure.ac to try krb5-config first before trying its built-in guesses at what the Kerberos libraries are. Because this requires rerunning autoconf, the debdiff also uses dh_autoreconf to do so.