stream_encoder.c : Fix an arithmetic overflow in the RICE2 partitioner.

For a specific 24 bit WAV file provided by Leigh Dyer

    http://lists.xiph.org/pipermail/flac-dev/2013-July/004284.html

encoding with compression level 7 was generating a file a couple of
orders of magintude larger than the original.

Debugging showed that variable abs_residual_partition_sum (a FLAC__uint32)
in function precompute_partition_info_sums_() was suffering from an
arithmetic overflowing on some 24 bit input files although this value
overflowing did not always cause larger output files.

Since the value abs_residual_partition_sum is eventually stored in an
array of FLAC__uint64, it makes sense to make abs_residual_partition_sum
a FLAC__uint64 anyway.

Debugging this problem was made easier by use of the Clang compiler's
-fsanitize=integer option.
src/libFLAC/bitwriter.c : Remove dead code.
Link with -no-undefined regardless of the OS

libFLAC* must never have undefined symbols no matter
what is the target platform.

Signed-off-by: Erik de Castro Lopo <erikd@mega-nerd.com>
src/share/grabbag/replaygain.c : Fix compiler warnings.

Gcc 4.8 has a new warning about use of un-initialized data. In particular
this new warning can detect if an automatic variable is defined in one function
and then passed to another and used before it is initialized.
Update .gitignore.
stream_encoder.c : Improve fix for arithmetic overflow.

The previous fix (patch 6f7ec60c) had the undesireable effect of slowing
down encoding speed on 16 bit files where the arithmetic overflow was
less likely to happen.

This fix forces the use of a FLAC__uint64 accumulator for 24 bit files
and restores the use of a FLAC_uint32 accumulator for 16 (and less) bit
files.

Unfortunately, I have not been able to prove to myself that this overflow
*cannot* happen with 16 bit files.
flac : Check compression ratio at end of encode process.

Stash the compression ratio in the EncoderSession struct and at the
end of the encode process, check if its > 1.0. Print an error message
if it is.