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

first pass at making an integer-only flavor of the libraries.  move FLAC__real out of ordinals.h to src/libFLAC/include/private/float.h, add FLAC__double and FLAC__float and use these everywhere instead of double and float, and don't typedef FLAC__real/float/double when building in integer-only mode.  still need to provide integer substitutes in several places.