fix bistream typos

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

doc/APIchanges

@@ -265,7 +265,7 @@ API changes, most recent first:
 
 2013-08-05 - 9547e3e / f824535 - lavc 55.22.100 / 55.13.0 - avcodec.h
   Deprecate the bitstream-related members from struct AVVDPAUContext.
-  The bistream buffers no longer need to be explicitly freed.
+  The bitsream buffers no longer need to be explicitly freed.
 
 2013-08-05 - 3b805dc / 549294f - lavc 55.21.100 / 55.12.0 - avcodec.h
   Deprecate the CODEC_CAP_HWACCEL_VDPAU codec capability. Use CODEC_CAP_HWACCEL

doc/muxers.texi

@@ -986,7 +986,7 @@ It is possible to specify to which streams a given bitstream filter
 applies, by appending a stream specifier to the option separated by
 @code{/}. @var{spec} must be a stream specifier (see @ref{Format
 stream specifiers}).  If the stream specifier is not specified, the
-bistream filters will be applied to all streams in the output.
+bitsream filters will be applied to all streams in the output.
 
 Several bitstream filters can be specified, separated by ",".