Increase the buffer size (and increments) for packing.

This should decrease the number of realloc calls and 
improve performance.

src/common/pack.h

@@ -46,7 +46,7 @@
 #include <string.h>
 
 #define BUF_MAGIC 0x42554545
-#define BUF_SIZE 4096
+#define BUF_SIZE (16 * 1024)
 
 struct slurm_buf {
 	uint32_t magic;