Add partial_tukey and punchout_tukey apodization functions

Adds two new apodization functions that seem to perform better than
the apodization functions currently in the codebase and fixes three
existing windows as well.

Its important to note that this patch only affects the encoder stage
that evaluates various possible predictors. Audio encoded with these
new windows will still decode with existing legacy decoders.

= Theory =
These functions are used to window the  audio data at the predictor
stage. These news functions enable the use of only part of the signal
to generate a predictor. This helps  because short transients can
introduce noise into the predictor. The  predictor becomes very good
at prediciting one part of the  signal, instead of mediocre for the
whole block.

Signed-off-by: Erik de Castro Lopo <erikd@mega-nerd.com>
win_utf8_io.c : Comment only.

Explains why flac is currently incompatible with extended-length paths.

Patch-from: lvqcl <lvqcl.mail@gmail.com>
Windows specific vsnprintf fixes.

* Changes flac_snprintf (in src/share/grabbag/snprintf.c) and its copy
  local_snprintf (src/libFLAC/metadata_iterators.c) to be almost sane.

* Adds flac_vsnprintf (src/share/grabbag/snprintf.c) and its copy
  local_vsnprintf (src/share/win_utf8_io/win_utf8_io.c).

* Changes stats_print_info in src/flac/utils.c so it uses flac_vsnprintf
  instead of vsnprintf. This makes return value checking unnecessary.

Patch-from: lvqcl <lvqcl.mail@gmail.com>