raise memory alarm threshold

The default 80% is just too low for many systems - I have less than
that on tanto most of the time.
It remains to be seen whether the new figure works ok for most users.

scripts/rabbitmq-server

@@ -69,6 +69,7 @@ erl \
     -os_mon start_memsup true \
     -os_mon start_os_sup false \
     -os_mon memsup_system_only true \
+    -os_mon system_memory_high_watermark 0.95 \
     -mnesia dir "\"${MNESIA_DIR}\"" \
     ${CLUSTER_CONFIG} \
     ${RABBIT_ARGS} \

scripts/rabbitmq-server.bat

@@ -110,6 +110,7 @@ set MNESIA_DIR=%MNESIA_BASE%/%NODENAME%-mnesia
 -os_mon start_memsup true ^
 -os_mon start_os_sup false ^
 -os_mon memsup_system_only true ^
+-os_mon system_memory_high_watermark 0.95 ^
 -mnesia dir \""%MNESIA_DIR%"\" ^
 %CLUSTER_CONFIG% ^
 %RABBIT_ARGS% ^