Improve warning message wording in WAV handler

Change "FmtExt chunk" into "extended part of fmt chunk", since there is
no such thing as a "FmtExt chunk".

(Mentioned in issue 3481510 by nu774, as "mysterious".)
Fix reading 64-bit float WAVs

Trying to read WAV files with 64-bit samples used to fail. Tell the WAV
handler that 8 bytes (64 bits) is an acceptable size for a sample.

Reported and analyzed by nu774 in issue 3481510.
splice: set output length to unknown, not 0

In the splice effect, the output length was only set (to unknown) when it
was not needed, immediately before returning with SOX_EFF_NULL. This
resulted in an incorrect output length of 0 when the effect had work to
do. Move the relevant line of code to a more appropriate place.
Increase maximum width for spectrograms

Spectrograms were arbitrarily limited to a width of 5000 pixels. This is
not a enough for all use cases, as demonstrated in a discussion on
sox-users. Now increased to 200000.
Deprecate ffmpeg format handler

Due to API changes in ffmpeg/libav, the ffmpeg format handler will soon
stop to compile (unless it is adapted to the new API, of course).
Mailing list discussion has shown that there is no interest in keeping
the handler; users should instead use the ffmpeg/avconf command line
utility via pipes.

Hence, mark the handler as deprecated in the changelog.
Fix compile error in oss.c

Depending on the implementation of fileno(), it doesn't accept a void
pointer as its argument. This could make the compiler fail.

Reported by Hans Petter Selasky in tracker item 3587421.
flac: dynamically (re)size encoder buffer

This avoids buffer overflows in an obvious way.  In the
common case, the malloc overhead is only incurred once as
callers rarely (never?) resize buffers within a flow.

ref: Buffer overrun during FLAC encoding - ID: 3474924
http://sourceforge.net/tracker/?func=detail&aid=3474924&group_id=10706&atid=110706
ladspa: free memory allocated for control ports

This memory is allocated during the getopts function and
needs to be freed to avoid memory leaks in long-running
libsox-based processes.
ladspa: call cleanup function if given

Some plugins have cleanup functions to deallocate memory after
instantiation.  This must be called after deactivate.
Update changelog
Fix soxi help message

Mention in soxi's help message that the bits per sample value (-b)
may be zero (e.g. for Vorbis encoding).
Minor documentation fixes
Fix truncation due to integer division

Found by Michael Niedermayer.

(cherry picked from commit 4d1529dd2d6af2632bcffa91dca29113422a489c)
Fix for autoconf 2.69
configure.ac: use AC_CONFIG_HEADERS

Use documented AC_CONFIG_HEADERS instead of AC_CONFIG_HEADER alias
that might be removed in future automake versions.

Related to tracker item 3600293, and to the previous commit.
dft_filter: use 64-bit numbers to count samples

(cherry picked from commit c276b0f734215afa7b5ce25086900552b06aad76)

Backported, as it fixes (the dft_filter part of) tracker item 3594822.
tempo: use 64-bit numbers to count samples

Use 64-bit numbers to count samples and segments in the tempo effect.

This fixes the bug reported in tracker item 3594822 by MrMod, where
  sox -V -S -r 192000 -n -n trim 0 3:15:00 tempo -q 0.9
would hang in an endless loop until memory exhaustion.
rate: don't hang if more than 2^31 output samples

The rate effect used to hang in an endless loop (until memory
exhaustion) when the number of output samples exceeded 2^31 (on
"normal" platforms; depending on size and signedness of size_t
and int), as in this example:
  sox -V -S -n -n trim 0 3:10:00 rate 192000
Use 64-bit numbers for counting samples, and don't subtract unsigned
numbers without checking.

Reported and analyzed by MrMod in tracker item 3592482. This same
problem is already fixed in the post-14.4.1 branch (commit c20cfab;
in conjunction with commit eb20581 for the 64-bit numbers).
Update changelog
Check for sys/stat.h when building with cmake

While we checked for sys/stat.h when building with the GNU toolchain,
this check was missing in the cmake configuration, and HAVE_SYS_STAT_H
was accordingly never set, whether the header file was present or not.