doxygen: dont generate docs for avconv.c

This is a workaround to avoid links in the ffmpeg.c documentation randomly pointing to
different code in avconv.c
This should be removed once doxygen is fixed and we upgraded
doxygen 1.7.3 is the latests i tested and that still has this issue.
Fixed Ticket421
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Doxyfile

@@ -625,7 +625,8 @@ EXCLUDE_SYMLINKS       = NO
 # for example use the pattern */test/*
 
 EXCLUDE_PATTERNS       = *.git \
-                         *.d
+                         *.d \
+                         avconv.c
 
 # The EXCLUDE_SYMBOLS tag can be used to specify one or more symbol names
 # (namespaces, classes, functions, etc.) that should be excluded from the