Merge libavcore into libavutil

Done to keep ABI compatible. Otherwise this is just silly

doc/APIchanges

@@ -2,7 +2,6 @@ Never assume the API of libav* to be stable unless at least 1 week has passed si
 the last major version increase.
 The last version increases were:
 libavcodec:  ?
-libavcore:   2010-07-21
 libavdevice: ?
 libavfilter: 2009-10-18
 libavformat: ?
@@ -13,6 +12,9 @@ libavutil:   2009-03-08
 
 API changes, most recent first:
 
+2011-02-15 - lavu 52.38.0 - merge libavcore
+  libavcore is merged back completely into libavutil
+
 2011-02-10 - 55bad0c - lavc 52.113.0 - vbv_delay
   Add vbv_delay field to AVCodecContext
 

doc/general.texi

@@ -986,7 +986,7 @@ you should only need to add the directory where the LIB files are installed
 (i.e. @file{c:\msys\usr\local\bin}). This is not a typo, the LIB files are
 installed in the @file{bin} directory. And instead of adding the static
 libraries (@file{libxxx.a} files) you should add the MSVC import libraries
-(@file{avcodec.lib}, @file{avformat.lib}, @file{avcore.lib}, and
+(@file{avcodec.lib}, @file{avformat.lib}, and
 @file{avutil.lib}). Note that you should not use the GCC import
 libraries (@file{libxxx.dll.a} files), as these will give you undefined
 reference errors. There should be no need for @file{libmingwex.a},