Core: don't reuse shared memory zone that changed ownership (ticket #210).

nginx doesn't allow the same shared memory zone to be used for different
purposes, but failed to check this on reconfiguration.  If a shared memory
zone was used for another purpose in the new configuration, nginx attempted
to reuse it and crashed.

src/core/ngx_cycle.c

diff --git a/src/core/ngx_cycle.c b/src/core/ngx_cycle.c
index f153729..e8b1559 100644
--- a/src/core/ngx_cycle.c
+++ b/src/core/ngx_cycle.c
@@ -447,7 +447,9 @@
                 continue;
             }
 
-            if (shm_zone[i].shm.size == oshm_zone[n].shm.size) {
+            if (shm_zone[i].tag == oshm_zone[n].tag
+                && shm_zone[i].shm.size == oshm_zone[n].shm.size)
+            {
                 shm_zone[i].shm.addr = oshm_zone[n].shm.addr;
 
                 if (shm_zone[i].init(&shm_zone[i], oshm_zone[n].data)