manual.xml: Add BZ_SEQUENCE_ERROR to return values of BZ2_bzDecompress

BZ_SEQUENCE_ERROR can be returned if BZ2_bzDecompress is called after
an earlier call already returned BZ_STREAM_END.

Reported-by: Vanessa McHale <vamchale@gmail.com>
diff --git a/manual.xml b/manual.xml
index 7c9e4ec..ba0480e 100644
--- a/manual.xml
+++ b/manual.xml
@@ -1583,6 +1583,8 @@
 BZ_STREAM_END
   if the logical end of the data stream was detected and all
   output in has been consumed, eg s-->avail_out > 0
+BZ_SEQUENCE_ERROR
+  if called after an earlier call already returned BZ_STREAM_END
 BZ_OK
   otherwise
 </programlisting>