SERVER-10486: mongofiles collection and chunk size

### Summary
This small patch adds support for
- setting an arbitrary collection name (help suggested that this was supported but the tool silently ignored it)
- setting the GridFS chunk size for a file during put
- a new command "re-chunk" that allows for changing the chunk size of existing files

### Ticket
The ticket for this pull request is at https://jira.mongodb.org/browse/SERVER-10486

This pull request supersedes/fixes/invalidates:
https://jira.mongodb.org/browse/SERVER-4931
https://jira.mongodb.org/browse/SERVER-2334
https://jira.mongodb.org/browse/SERVER-6874
https://jira.mongodb.org/browse/SERVER-2335
https://jira.mongodb.org/browse/SERVER-2469

### lint check output
    # python buildscripts/lint.py src/mongo/tools/files.cpp 
    Total errors found: 0

I'd appreciate if this could be merged for a future version of MongoDB.