client: Fixed regression introduced by adding a new parameter to the...

client: Fixed regression introduced by adding a new parameter to the OpenFile() method: truncate with a new file size != 0 were not successful. Removed the internal OpenFile() method to OpenFileWithTruncateSize() to reduce the probability this error will happen again.

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@3614 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534