client: Options class:

- Added advanced option "enable_atime" which is false by default. If set to false, a future version of the libxtreemfs will ignore setAttr() calls which only change the ATIME field.
- Added TODO note in FuseAdapter to take care of enable_atime option.
- Made gridmap usermapping options visible for WIN32.

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@3569 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534