cups-filters 2.0rc1

Release Candidate: Fixes for bugs found by Coverity check run, plus some more fixes.

• foomatic-rip: Fix a SIGPIPE error when calling gs (Pull request #517)
  Ubuntu's autopkgtest for foo2zjs shows foo2zjs's testsuite failing with cups-filters 2.0beta3 on ppc64el. This is cause by a timing issue in foomatic-rip which is fixed now.
• Coverity check done by Zdenek Dohnal for the inclusion of cups-filters 2.x in Fedora and Red Hat. Zdenek has fixed all the issues: Missing free(), files not closed, potential string overflows, ... Thanks a lot! (Pull request #510).
• Dropped all C++ references and obsolete C standards (Pull requests #504 and #513)
  With no C++ compiler needed, there is no need for any checks or setting for C++ in configure.ac.
• configure.ac: Change deprecated AC_PROG_LIBTOOL for LT_INIT (Pull request #508)