on Windows 64-bit, maybe we should default to a better maxBBufSize in MMapDirectory [LUCENE-2832]

Currently the default max buffer size for MMapDirectory is 256MB on 32bit and Integer.MAX_VALUE on 64bit:

```
public static final int DEFAULT_MAX_BUFF = Constants.JRE_IS_64BIT ? Integer.MAX_VALUE : (256 * 1024 * 1024);
```

But, in windows on 64-bit, you are practically limited to 8TB. This can cause problems in extreme cases, such as: http://www.lucidimagination.com/search/document/7522ee54c46f9ca4/map_failed_at_getsearcher

Perhaps it would be good to change this default such that its 256MB on 32Bit **OR** windows, but leave it at Integer.MAX_VALUE
on other 64-bit and "64-bit" (48-bit) systems.

---
Migrated from [LUCENE-2832](https://issues.apache.org/jira/browse/LUCENE-2832) by Robert Muir (@rmuir), updated May 09 2016
Attachments: [LUCENE-2832.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-2832/LUCENE-2832.patch)