Use FILE * instead of fd for files to support buffering

file.c

formats/format_au.c

formats/format_g723.c

formats/format_g726.c

formats/format_g729.c

formats/format_gsm.c

formats/format_h263.c

formats/format_ilbc.c

formats/format_ogg_vorbis.c

formats/format_pcm.c

formats/format_pcm_alaw.c

formats/format_sln.c

formats/format_vox.c

formats/format_wav.c

formats/format_wav_gsm.c

include/asterisk/channel.h

include/asterisk/file.h