Increase journalling capacity limits

ISSUE SUMMARY
On MongoDB with the MMAPv1 storage engine, the journalling subsystem warns about large updates exceeding 128MB for 32-bit systems and 256MB for 64-bit systems as follows:

warning assertion failure a <= 256*1024*1024 src/mongo/util/alignedbuilder.cpp

Concurrent operations updating large documents may exceed the maximum journalling capacity of 256MB for 32-bit systems and 512MB for 64-bit systems. When that limit is exceeded the server shuts down with a log message like the following:

Assertion failure a <= 512*1024*1024 src/mongo/util/alignedbuilder.cpp 

RESOLUTION DETAILS
MongoDB versions 3.0.1 and above increase the limits for the journalling capacity for 64-bit systems to warn at 512MB, and shut down at 2000MB with a message like the following:

I - [durability] error writing journal: too much uncommitted data (2098200576 bytes)

I - [durability] shutting down immediately to avoid corruption

I - [durability] Fatal Assertion 28614

The journalling capacity limits for 32-bit systems remain unchanged.