flac++.pc.in: Make flac a private requires

Patch pulled from Debian package.

Description:
Chain::Status::as_cstring uses FLAC__Metadata_ChainStatusString which
is in libFLAC. Since the function is inline, every program calling
this function must also link with -lflac, but this is missing in
flac++.pc.

Bug-Debian: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=713645

src/libFLAC++/flac++.pc.in

@@ -6,6 +6,6 @@ includedir=@includedir@
 Name: FLAC++
 Description: Free Lossless Audio Codec Library (C++ API)
 Version: @VERSION@
-Requires.private: flac
+Requires: flac
 Libs: -L${libdir} -lFLAC++
 Cflags: -I${includedir}