merged patches from Chris Csanady and John Steele Scott, better checking for altivec and ppc64 on ppc

libFLAC++: all metadata object operator=() funcs now return *this; add Metadata::*::assign() and FLAC::Metadata::get_tags()

add vorbiscomment validation functions to format.c and test code; validate name part of vorbiscomment in metadata and metadata++ interfaces

additions to metadata object api: more vorbiscomment functions, trailing-null on vorbis comment field values enforced everywhere

split PPC asm code into two directores, one holding asm compatible with OS X native 'as', and one for 'gas'

finished integerized flavor of library; sections with floating point are either #ifdef'd out or written in fixed-point