Fixed FTBFS caused by ruby 2.1 (Debian/testing).

qtruby/rubylib/qtruby/configure.in.in

@@ -26,6 +26,12 @@ else
         RUBY_CFLAGS=`$PKGCONFIG ruby-2.0 --cflags`
       fi
     fi
+    if test -z "$RUBY_VERSION"; then
+      RUBY_VERSION=`$PKGCONFIG ruby-2.1 --modversion 2>/dev/null`
+      if test -n "$RUBY_VERSION"; then
+        RUBY_CFLAGS=`$PKGCONFIG ruby-2.1 --cflags`
+      fi
+    fi
     if test -z "$RUBY_VERSION"; then
       # pkgconfig file does not exist but might be 1.9.1: RUBY_VERSION defined in ruby/version.h
       if test -n "$RUBY -r rbconfig -e 'printf("%s",RbConfig::CONFIG@<:@"rubyhdrdir"@:>@)'"; then