Write out all of the available bits when using Z_BLOCK.

Previously, the bit buffer would hold 1 to 16 bits after "all" of the
output is provided after a Z_BLOCK deflate() call.  Now at most seven
bits remain in the output buffer after Z_BLOCK.  flush_pending() now
flushes the bit buffer before copying out the byte buffer, in order
for it to really flush as much as possible.

trees.c

@@ -876,6 +876,15 @@ void ZLIB_INTERNAL _tr_stored_block(s, buf, stored_len, last)
     copy_block(s, buf, (unsigned)stored_len, 1); /* with header */
 }
 
+/* ===========================================================================
+ * Flush the bits in the bit buffer to pending output (leaves at most 7 bits)
+ */
+void ZLIB_INTERNAL _tr_flush_bits(s)
+    deflate_state *s;
+{
+    bi_flush(s);
+}
+
 /* ===========================================================================
  * Send one empty static block to give enough lookahead for inflate.
  * This takes 10 bits, of which 7 may remain in the bit buffer.